Mogollon Highlands Research Articles

The Mogollon Highlands Ecoregion of the American Southwest: A Neglected Center of Ecological Diversity

The Mogollon Highlands Ecoregion of the American Southwest: A Neglected Center of Ecological Diversity

An Ecoregional Conservation Assessment for Forests and Woodlands of the Mogollon Highlands Ecoregion, Northcentral Arizona and Southwestern New Mexico, USA

The Mogollon Highlands, Arizona/New Mexico, USA, spans a large biogeographical region of 11 biotic communities, 63 land cover types, and 7 ecoregions. This 11.3 M ha region has high levels of beta diversity across topo-edaphic gradients that span deserts to mountain tops. The main stressors affecting the region’s forests and woodlands include climate change, livestock grazing, and frequent mechanical removals of large amounts of forest biomass for fire concerns. We present an ecoregion conservation assessment for robust conservation area design that factors in appropriate wildfire response to protect communities from increasing threats of climate-induced wildfires spreading into urban areas. We focused mainly on maintaining connectivity for endangered focal species (grizzly bear (Ursus arctos horribilis) and Mexican wolf (Canis lupus baileyi)) along with protecting mature and old-growth (MOG) forests, Piñon (Pinus spp.)–Juniper (Juniperus spp.) Woodlands, and riparian areas. Over half the region is managed by federal agencies where new protected areas can be integrated with tribal co-management and prescribed burning, defensible space, and home hardening to protect communities from the growing threat of climate-induced wildfires. However, just 9% of the study area is currently protected, and even with the inclusion of proposed protected areas, only 24% would be protected, which is below 30 × 30 targets. The potential grizzly bear habitat, wolf habitat connectivity, and MOG forests (1.6 M ha (14.2%) of the study area; 18% protected) are concentrated mainly in the central and eastern portions of the MHE. There were 824 fires (2 to 228,065 ha) from 1984–2021, with 24% overlapping the wildland–urban interface. Regional temperatures have increased by 1.5 °C, with a 16% reduction in precipitation and stream flow since 1970 that under worst-case emission scenarios may increase temperatures another 3 to 8 °C by the century’s end. The unique biodiversity of the MHE can be better maintained in a rapidly changing climate via at least a three-fold increase in protected areas, co-management of focal species with tribes, and strategic use of fuel treatments nearest communities.

Challenging assumptions of sediment routing in retroarc foreland basins: Detrital zircon evidence for axial versus transverse drainages in the Late Cretaceous of southern Utah, USA

AbstractDepositional models for retroarc foreland basin systems commonly imply a direct link between thrust belt dynamics and sediment supply, despite documented complexity between orogen‐transverse and orogen‐parallel (axial) sediment routing systems. Previous detrital zircon provenance studies from the Straight Cliffs Formation in the Kaiparowits Plateau of southern Utah indicate primary axial source areas to the south (Mogollon Highlands), and southwest (Cordilleran magmatic arc), with relatively minor transverse input from the Sevier fold‐thrust belt to the west. Complementary data from 32 new samples are presented to investigate whether these trends persist in correlated strata from sections most proximal to the active fold‐thrust belt, as well as strata proximal to the Mogollon Highlands. This study aims to improve statistical robustness through higher‐n datasets (>300 analyses/sample) and addresses the possibility of recycling of zircon grains from strata in the exhumed Sevier fold‐thrust belt. Based on this provenance dataset, we infer that orogen‐transverse deposition was mainly limited to the most proximal sections (within ca. 75 km of the fold‐thrust belt), but included episodic distribution across the foredeep that was associated with distinct intervals of widespread amalgamated sand and gravel sheet deposits. In contrast, more distal parts of the foredeep record long‐distance fluvial transport (>400 km) of zircons from the active Cordilleran magmatic arc as well as Yavapai‐Mazatzal basement rocks in central Arizona (the Mogollon Highlands). Palaeogeographic reconstructions suggest the apex of a large basin‐axial fluvial system may have been located at the structural syntaxis between the Sevier fold‐thrust belt and western margin of the Mogollon Highlands. This interpretation is supported by detrital zircon data presented here, thus extending the possibility that the Palaeogene ‘California River’ may have existed by at least Late Cretaceous time. Ultimately, these data point to extrabasinal controls on sediment supply, which was largely decoupled from flexural accommodation controls in this archetype retroarc foreland basin.

Neogene drainage reversal and Colorado Plateau uplift in the Salt River area, Arizona, USA

UPb detrital zircon and 40Ar39Ar detrital sanidine dating of paleoriver deposits refines the timing of the mid-Cenozoic drainage reversal from NE- to SW-flowing rivers across the southern edge of the Colorado Plateau. NE-flowing paleorivers of the Mogollon Rim Formation were of multiple ages: ≤59.38 Ma for the Flying V outcrop and ≤37–33 Ma for other outcrops. These NE-flowing paleorivers were defeated by construction of the 38–23 Ma Mogollon–Datil volcanic field and extensional collapse of the Mogollon Highlands. The 37.6–21.8 Ma Whitetail Conglomerate of the Salt River paleocanyon records the transition from NE-flowing rivers to internal drainage that persisted from 30 to 14.67 Ma during continued extensional collapse. The SW-flowing proto-Salt River was established by about 12 Ma and flowed into Tonto Basin ~7 Ma. The Salt River extended its length to near Phoenix via basin spillover from the Tonto and Verde basins about 2.8 Ma and became established in its present path only in the past ~500 ka. Between 3.0 and 0.52 Ma, incision rates of the Salt River's headwaters have been steady at 95 m/Ma as calculated using the age and height of four far-traveled basalt runouts from the Springerville volcanic field. These incision rates contrast with 10 m/Ma rates for downstream areas near the Sentinel-Arlington volcanic field on the Gila River over the past 2.37 Ma. This 85 m/Ma of differential incision was a geomorphic response of headwater drainages to changes in base level (base level fall plus headwater uplift) that, at least in part, was a consequence of top-down integration of the Salt and Verde river systems via spillover. Neogene headwater uplift is proposed to have set the stage for and perhaps driven this downward integration by increasing river gradients, and progressive uplift in the past 3 Ma may help explain post-integration steady headwater incision. Surface uplift components include construction of the Springerville and San Francisco volcanic fields and related mantle-driven epeirogenic uplift of the southern rim of the Colorado Plateau. Long-term differential incision rates for the Salt River (85 m/Ma) are less than for the Colorado River system (140 m/Ma across Grand Canyon) suggesting west-up neotectonic tilting of the Colorado Plateau.

Age constraint for the Moreno Hill Formation (Zuni Basin) by CA-TIMS and LA-ICP-MS detrital zircon geochronology.

The “mid-Cretaceous” (~125–80 Ma) was punctuated by major plate-tectonic upheavals resulting in widespread volcanism, mountain-building, eustatic sea-level changes, and climatic shifts that together had a profound impact on terrestrial biotic assemblages. Paleontological evidence suggests terrestrial ecosystems underwent a major restructuring during this interval, yet the pace and pattern are poorly constrained. Current impediments to piecing together the geologic and biological history of the “mid-Cretaceous” include a relative paucity of terrestrial outcrop stemming from this time interval, coupled with a historical understudy of fragmentary strata. In the Western Interior of North America, sedimentary strata of the Turonian–Santonian stages are emerging as key sources of data for refining the timing of ecosystem transformation during the transition from the late-Early to early-Late Cretaceous. In particular, the Moreno Hill Formation (Zuni Basin, New Mexico) is especially important for detailing the timing of the rise of iconic Late Cretaceous vertebrate faunas. This study presents the first systematic geochronological framework for key strata within the Moreno Hill Formation. Based on the double-dating of (U-Pb) detrital zircons, via CA-TIMS and LA-ICP-MS, we interpret two distinct depositional phases of the Moreno Hill Formation (initial deposition after 90.9 Ma (middle Turonian) and subsequent deposition after 88.6 Ma (early Coniacian)), younger than previously postulated based on correlations with marine biostratigraphy. Sediment and the co-occurring youthful subset of zircons are sourced from the southwestern Cordilleran Arc and Mogollon Highlands, which fed into the landward portion of the Gallup Delta (the Moreno Hill Formation) via northeasterly flowing channel complexes. This work greatly strengthens linkages to other early Late Cretaceous strata across the Western Interior.

LA-ICPMS U–Pb geochronology of detrital zircon grains from the Coconino, Moenkopi, and Chinle formations in the Petrified Forest National Park (Arizona)

Abstract. Uranium–lead (U–Pb) geochronology was conducted by laser ablation – inductively coupled plasma mass spectrometry (LA-ICPMS) on 7175 detrital zircon grains from 29 samples from the Coconino Sandstone, Moenkopi Formation, and Chinle Formation. These samples were recovered from ∼ 520 m of drill core that was acquired during the Colorado Plateau Coring Project (CPCP), located in Petrified Forest National Park (Arizona). A sample from the lower Permian Coconino Sandstone yields a broad distribution of Proterozoic and Paleozoic ages that are consistent with derivation from the Appalachian and Ouachita orogens, with little input from local basement or Ancestral Rocky Mountain sources. Four samples from the Holbrook Member of the Moenkopi Formation yield a different set of Precambrian and Paleozoic age groups, indicating derivation from the Ouachita orogen, the East Mexico arc, and the Permo-Triassic arc built along the Cordilleran margin. A total of 23 samples from the Chinle Formation contain variable proportions of Proterozoic and Paleozoic zircon grains but are dominated by Late Triassic grains. LA-ICPMS ages of these grains belong to five main groups that correspond to the Mesa Redondo Member, Blue Mesa Member and lower part of the Sonsela Member, upper part of the Sonsela Member, middle part of the Petrified Forest Member, and upper part of the Petrified Forest Member. The ages of pre-Triassic grains also correspond to these chronostratigraphic units and are interpreted to reflect varying contributions from the Appalachian orogen to the east, Ouachita orogen to the southeast, Precambrian basement exposed in the ancestral Mogollon Highlands to the south, East Mexico arc, and Permian–Triassic arc built along the southern Cordilleran margin. Triassic grains in each chronostratigraphic unit also have distinct U and thorium (Th) concentrations, which are interpreted to reflect temporal changes in the chemistry of arc magmatism. Comparison of our LA-ICPMS ages with available chemical abrasion thermal ionization mass spectrometry (CA-TIMS) ages and new magnetostratigraphic data provides new insights into the depositional history of the Chinle Formation, as well as methods utilized to determine depositional ages of fluvial strata. For parts of the Chinle Formation that are dominated by fine-grained clastic strata (e.g., mudstone and siltstone), such as the Blue Mesa Member and Petrified Forest Member, all three chronometers agree (to within ∼ 1 Myr), and robust depositional chronologies have been determined. In contrast, for stratigraphic intervals dominated by coarse-grained clastic strata (e.g., sandstone), such as most of the Sonsela Member, the three chronologic records disagree due to recycling of older zircon grains and variable dilution of syn-depositional-age grains. This results in LA-ICPMS ages that significantly predate deposition and CA-TIMS ages that range between the other two chronometers. These complications challenge attempts to establish a well-defined chronostratigraphic age model for the Chinle Formation.

Fire regimes and structural changes in oak-pine forests of the Mogollon Highlands ecoregion: Implications for ecological restoration

Ponderosa pine (Pinus ponderosa) forests occur at their warmer, drier environmental limits in the Mogollon Highlands ecoregion (MHE) of the Southwestern United States, and are commonly found in stringers or discrete stands that form ecotones with interior chaparral. These “rear edge” forests are likely to be highly vulnerable to rapid changes in structure and composition with climate warming, drought, and wildfire. There is increasing interest in understanding historical conditions, ecosystem changes, and restoration needs for MHE forests. However, comprehensive reconstruction analysis of fire regimes and stand structure has not been done for these systems, which differ from many montane ponderosa pine forests by having an abundance of understory shrubs. In this study we used demographic data from field plots, fire scar samples, and dendroecology to reconstruct historical fire regimes and landscape structure at ponderosa pine-dominated sites that spanned a range of environmental conditions on the Prescott and Tonto National Forests. We found strong evidence of historical surface fire regimes with mean fire intervals ranging 1.3–15.6 years across the five MHE sites during the period 1700–1879. We found very little evidence of historical high-severity fire at any study site. Historical forest structure was open with tree densities ranging 84.7–136.4 trees ha−1 and stand basal area (BA) ranging 4.5–8.4 m2 ha−1. Historical composition showed codominance of ponderosa pine, Arizona white oak (Quercus arizonica), Emory oak (Q. emoryi), and Gambel oak (Q. gambelii). Thus, oak species and likely other hardwoods were important historical components of these ecosystems. Contemporary forests are greater in stand density and BA by 359–703% and 285–502%, respectively, compared to historical estimates. In addition, we observed contemporary shifts in species composition. Changes related to disruption of historical fire regimes have increased susceptibility of ponderosa pine forests in the MHE to rapid shifts in structure and composition that may come about with climate change and high-intensity wildfire. Meeting fuels reduction and ecological restoration goals will be challenging for land managers due to vigorous regeneration responses of shrubs to tree thinning, prescribed burning, or other management activities. Managers will be required to balance attention to historical reference conditions, conservation of biological diversity, and needs for fuels management.

Smudged Wares: The Importance of Color and Iridescence as a Long-Lived Decorative Attribute in the Mogollon Highlands

The importance of color and iridescences as decorative attributes is rising in importance in archaeological theory. Following this trend, this study examines smudged vessels dating to the Reserve and Tularosa phases (AD 1000–1250) from central Arizona and New Mexico. Smudging is created by the use of polish and the manipulation of firing atmosphere resulting in a black, iridescent surface. It has long been assumed to be functional, but the decorative aspects of smudging are understudied. I argue that smudging is a decorative method first used in AD 400 that formed the foundation of a long-lived decorative canon lasting until at least AD 1250/1350. To better understand this decorative tradition, a discussion of style (with an emphasis on color and iridescence) and ethnoarchaeological studies on the manipulation of firing atmosphere are reviewed. This is followed by an examination of the distribution of smudged wares in the Southwest, its rising popularity in the Pinelawn/Reserve area through time and a formal analysis of 506 smudged bowls demonstrating its use on bowls used for a variety of functions ranging from miniature vessels to household use to feasting bowls.

Basin‐axial progradation of a sediment supply driven distributive fluvial system in the Late Cretaceous southern Utah foreland

AbstractThe Turonian‐Coniacian Smoky Hollow Member of the Straight Cliffs Formation in the Kaiparowits basin of southern Utah records a stratigraphic transition from isolated fluvial channel bodies to increasingly amalgamated channel belts capped by the Calico bed, a sheet‐like sand‐gravel unit. Characteristics of the Smoky Hollow Member are consistent with a prograding distributive fluvial system including: up‐section increases in average grain size, bed thickness, channel‐body amalgamation, a fan‐shaped planform morphology and a downstream increase in channel sinuosity. The system prograded to the northeast based on thickness and facies patterns, and palaeocurrent indicators. This basin‐axial sediment‐dispersal trend, which was approximately parallel to the fold‐thrust belt at this latitude, is supported by provenance data including detrital zircons and modal sandstone compositions indicating sediment derivation mainly from the Mogollon Highlands and Cordilleran magmatic arc to the southwest, with episodic input from the more proximal Sevier fold‐thrust belt to the west. Progradation occurred during a eustatic still‐stand, relatively stable climatic conditions, and continuous tectonic subsidence, thus suggesting increased extrabasinal sediment supply as a primary control on basin‐fill. Progradation of the Smoky Hollow Member fluvial system culminated in a ~2–3 My hiatus at the top of the lower Calico bed. Correlation with the Notom delta of the Ferron Sandstone, 80 km northeast in the Henry basin, is proposed on the basis of facies relationships and geochronology. The Calico bed unconformity is linked to regional tectonically driven tilting and erosion observed in both basins.

Interactions between axial and transverse drainage systems in the Late Cretaceous Cordilleran foreland basin: Evidence from detrital zircons in the Straight Cliffs Formation, southern Utah, USA

New detrital zircon geochronologic data from the Straight Cliffs Formation of southern Utah provide insight into the controls on stratigraphic architecture of the Western Interior Basin during Turonian–early Campanian time. Detrital zircon ages ( N = 40, n = 3650) derived from linked fluvial and shallow-marine depositional systems of the Kaiparowits Plateau indicate the majority of zircons in fluvial strata were derived from the Mogollon Highlands (1.25–1.90 Ga, 67% of fluvial zircons), with subordinate contributions delivered from the Sevier fold-and-thrust belt (265–1250 Ma, 17%) and Cordilleran magmatic sources (81–265 Ma, 16%). Integration of these data with fluvial facies distributions, petrography, clast counts, and evidence of magmatic arc sources from the Mohave region of California implies the presence of a northeast-flowing, axial fluvial system. This system was fed by rivers draining the Mogollon Highlands to the south and by transverse drainages from the Sevier fold-and-thrust belt to the west. Compared to the fluvial deposits, shallow-marine sandstones have a greater proportion of Sevier fold-and-thrust belt–derived zircons (42%), which were delivered via longshore currents from the north. Shallow-marine samples also contain less Mogollon input (44%) compared to contemporaneous fluvial systems, and similar input from the magmatic arc (14%). Although Proterozoic zircons associated with the Mogollon Highlands are also present in the Sevier fold-and-thrust belt, several lines of evidence argue for a distinct southerly source for the Straight Cliffs Formation. These include (1) moderate proportions of feldspar and angular quartz grains in fluvial sandstones, which favor a felsic intrusive source, and (2) prominent 1.4 and 1.7 Ga zircon populations. The 1.4 and 1.7 Ga peaks are the only dominant Proterozoic peaks in samples from the Straight Cliffs Formation, whereas samples derived more directly from the Sevier fold-and-thrust belt tend to have a broader distribution of Proterozoic age peaks. Up-section architectural trends in the Straight Cliffs Formation are linked to trends in detrital zircon geochronologic data, underscoring the likelihood of common drivers and controls. The axial system depositing Straight Cliffs fluvial strata was primarily fed by drainages originating in the Mogollon Highlands during a pulse of tectonic activity in the Maria fold-and-thrust belt and generally high subsidence rates in the foreland basin (Turonian–Santonian). Over time, activation of the Paxton duplex in the Sevier fold-and-thrust belt (early Campanian) exhumed proximal foreland basin strata and enabled drainage systems from the Sevier fold-and-thrust belt to feed into the basin more prominently. The results presented here underscore the potential significance of axial fluvial systems and their complex interplay with transverse drainage networks in foreland basins.

Late Cretaceous Fluvial-Megafan and Axial-River Systems In the Southern Cordilleran Foreland Basin: Drip Tank Member of Straight Cliffs Formation and Adjacent Strata, Southern Utah, U.S.A

Abstract The Upper Cretaceous (lower Campanian) Drip Tank Member of the Straight Cliffs Formation in the Grand Staircase region of southern Utah is an upward-coarsening, sandstone-rich, low-sinuosity fluvial deposit in the Cordilleran foreland basin. The Drip Tank Member thins from 75 m to 30 m eastward across the basin foredeep, approximately parallel to its dominant eastward sediment-dispersal direction, and thins southward along the foredeep to as little as 17 m near its southern outcrop extent along modern cliff lines. It overlies and underlies mudstone-rich fluvial strata of the John Henry Member of the Straight Cliffs Formation and lower member of the Wahweap Formation, respectively, both of which were deposited by northeast-flowing rivers. The John Henry–Drip Tank contact lies in an interfingering, progradational stratigraphic transition from medium-grained lenticular sandstone bodies to tabular coarse-grained amalgamated sandstone bodies. The contact with the overlying Wahweap Formation is locally a prominent surface of erosion or sediment reworking. Sandstone petrography and detrital-zircon age populations of the strata indicate detrital sources in basement south of the foreland basin, thrust sheets to the west, and magmatic arc rocks to the southwest. The uppermost part of the John Henry Member contains as much as 10% feldspar and abundant ∼ 1.84–1.60 Ga detrital zircons derived from Yavapai–Mazatzal basement rocks in the Mogollon Highlands. The Drip Tank Member ranges from quartzarenite to chert-bearing sublitharenite with Grenville (∼ 1.2–1.1 Ga), Neoproterozoic and early Paleozoic detrital zircons derived from Proterozoic through Jurassic strata exposed in the Sevier orogenic belt. Lower member Wahweap litharenites contain abundant thrust-belt-derived detrital carbonate grains absent from compositionally mature Drip Tank sandstones, as well as a broad range of zircon ages. The Drip Tank Member constitutes deposits of a sand-rich, fluvial megafan, or distributive fluvial system, that displaced a subjacent, but partly time-equivalent axial-fluvial system eastward as the megafan, driven in part by seasonally high discharge fed by monsoonal precipitation, prograded across the basin foredeep. A thick, amalgamated fan-axis succession present in northern exposures contrasts with a thinner fan-flank succession in southern localities. Tabular sixth–order lithosomes, each containing channels on the order of 7 m deep, define three individual fluvial fans or fan lobes in the megafan system. Younger Wahweap fluvial channels eroded uppermost Drip Tank deposits of the fan axis and fan flank. Transverse fan progradation across the foredeep recorded falling accommodation/sediment supply in an aggradational to progradational systems tract. Erosion and reworking of the upper fan surface record decreased accommodation, sediment bypass, and erosion prior to reoccupation of the foredeep by the Wahweap axial-fluvial system. The upper contact of the Drip Tank Member is thus the primary sequence boundary in this multi-component fluvial system, and the lower Wahweap represents transitional systems-tract deposits accumulated as accommodation/sediment supply increased.

Identifying the Origin of Southwestern Shell: A Geochemical Application to Mogollon Rim Archaeomolluscs

Archaeological marine shell artifacts moving over long distances may reveal the remnants of social networks, social currency, and the nuances of exchange. For the southwestern United States and northern Mexico, potential sources of marine shell are predominantly the Gulf of California and Pacific Ocean. There exists some taxonomic overlap between molluscan communities of these regions and the Gulf of California, necessitating non-biogeographic methods to distinguish their origins. Combined oxygen and carbon stable isotope ratio measurements demonstrate that modern shells from these water bodies have distinct isotopic ranges. Molluscan isotopie composition within the Gulf of California varies, which allows for the identification of distinct source regions. Archaeological marine shell from Pueblo III and IV sites in the Mogollon Rim region of east-central Arizona are sourced, demonstrating that archaeological shell was obtained from a northeastern subregion of the Gulf of California. This is the closest source for the Puebloan communities, but it is not consistent with previous hypotheses concerning the origin of marine shell in the Colorado Plateau and Mogollon Highlands, which suggested an exchange route via Paquime originating south of Isla Tiburon. We discuss the implications of these results in the context of previous research and draw conclusions about the meaning of shell use in the region.

Detrital zircon geochronology of Cordilleran retroarc foreland basin strata, western North America

AbstractWe present a compilation of 8717 U‐Pb analyses from 95 detrital zircon samples of Jurassic‐Eocene North American Cordillera foreland basin strata. Of these samples, 30 are new and previously unpublished. Variation in detrital zircon age spectra between samples records erosion or recycling of basement and cover rocks within the Cordilleran orogenic wedge. Each sample can be classified into one of six major provenance groups, whose age spectra suggest derivation from (1) Mesozoic eolianites of the western United States, (2) Paleozoic passive margin strata of the western United States, (3) Paleozoic passive margin strata of western Canada, (4) the Mogollon Highlands, (5) the Cordilleran magmatic arc, or (6) Yavapai‐Mazatzal Province crystalline basement rocks. Referencing these provenance interpretations to their location and stratigraphic deposition age produces a detailed spatial and temporal record of sediment dispersal within the foreland basin system. Late Jurassic provenance is dominated by recycling of Mesozoic eolianites from sources in the Sevier thrust belt. Cretaceous‐Eocene provenance is dominated by recycling of the passive margin, with increasing complexity upsection. We interpret that this provenance transition records a basin‐wide unroofing sequence. A composite age‐probability plot of 1539 young (<250 Ma) detrital zircons reveals at least four age‐abundance peaks that we interpret to represent periodic high‐flux magmatism in the Cordilleran arc.

Identifying the Origin of Southwestern Shell: A Geochemical Application to Mogollon Rim Archaeomolluscs

Archaeological marine shell artifacts moving over long distances may reveal the remnants of social networks, social currency, and the nuances of exchange. For the southwestern United States and northern Mexico, potential sources of marine shell are predominantly the Gulf of California and Pacific Ocean. There exists some taxonomic overlap between molluscan communities of these regions and the Gulf of California, necessitating non-biogeographic methods to distinguish their origins. Combined oxygen and carbon stable isotope ratio measurements demonstrate that modern shells from these water bodies have distinct isotopic ranges. Molluscan isotopie composition within the Gulf of California varies, which allows for the identification of distinct source regions. Archaeological marine shell from Pueblo III and IV sites in the Mogollon Rim region of east-central Arizona are sourced, demonstrating that archaeological shell was obtained from a northeastern subregion of the Gulf of California. This is the closest source for the Puebloan communities, but it is not consistent with previous hypotheses concerning the origin of marine shell in the Colorado Plateau and Mogollon Highlands, which suggested an exchange route via Paquime originating south of Isla Tiburon. We discuss the implications of these results in the context of previous research and draw conclusions about the meaning of shell use in the region.

Detrital zircons indicate no drainage link between southern California rivers and the Colorado Plateau from mid-Cretaceous through Pliocene

Central to debate about the age, origin, and evolution of Grand Canyon (southwestern United States) is the history of the Colorado River and its precursors. Reversal of dextral slip along the San Andreas fault system since the early Pliocene restores southern California to the downstream end of the Colorado River. If the Colorado River flowed to the Pacific Ocean prior to 6 Ma, then its sand would have the distinctive detrital-zircon age distributions of upper Paleozoic and Mesozoic strata of the Colorado Plateau, which contain 30%–46% 300–1100 Ma zircon originally transported from orogenic belts of southeastern Laurentia. In contrast, age distributions of 6662 detrital zircons from 167 Upper Cretaceous–Pliocene sandstone samples from southern California average 44%–88% Cretaceous, with only 0.4%–1.3% 300–1100 Ma grains, most of which can be attributed to local recycling from older deposits. No individual Upper Cretaceous to Pliocene sandstone sample from southern California contains >3% 300–1100 Ma zircon. Although Paleogene headwaters of southern California rivers extended into the eastern Mojave Desert, Sonoran Desert, and Mogollon Highlands, our results indicate that these headwaters did not extend as far as the Colorado Plateau. This conclusion conflicts with the hypothesis of a Paleogene southwest-flowing Arizona River, but supports late Miocene–Pliocene drainage reorganization and integration of the Colorado River coincident with development of the Salton Trough and Gulf of California.

Carbonate facies of the Upper Triassic Ojo Huelos Member, San Pedro Arroyo Formation (Chinle Group), southern New Mexico: Paleoclimatic implications

The Upper Triassic (Adamanian LVF) Ojo Huelos Member of the San Pedro Arroyo Formation (Chinle Group) is a distinctive, carbonate-rich unit that occurs in the lower Chinle section of central New Mexico. The member consists mainly of micritic lime mudstones, ostracodal wackestones to grainstones, peloidal grainstones and distinctive pisolitic rudstones, interbedded with fine-grained siliciclastic mudstones. Most limestones exhibit some evidence of pedogenic brecciation and root penetration, and porous fabrics similar to those of modern limestone tufas occur locally. The interbedded mudstones are typically lenticular and commonly display a blocky ped fabric in which subequant peds are separated by sparry calcite veins. Fossils from the Ojo Huelos Member are freshwater (darwinulid) ostracodes, various freshwater fishes and aquatic/amphibious tetrapods–metoposaurs and phytosaurs. We interpret the carbonate facies as the deposits of carbonate lakes, ponds and wetlands that were partly spring-fed, whereas the interbedded and surrounding mudstones were alluvial in origin. The groundwater and overland hydrology of the region was likely controlled by the relative proximity to an upland recharge area in the Mogollon Highlands to the south, but sedimentary fabrics record strong overprinting by desiccation and pedogenic reworking. Consequently, we interpret the Ojo Huelos Member as recording a climate that varied from subhumid to semi-arid, which caused episodic falls in the hydrologic base-level. This resulted in landscape degradation, exemplified by significant pedogenic and erosional reworking of the carbonate sediments and fluvial incision.

A new Vaejovis from the Mogollon Highlands of northern Arizona (Scorpiones: Vaejovidae)

A new scorpion species, Vaejovis halli sp. nov., is described. This relatively small, brown new species is found on Mount Ord in the Mazatzal Mountains along the Mogollon Rim of northern Arizona. The new species appears most similar to V. vorhiesi Stahnke and V. deboerae Ayrey. The most distinguishing characteristic of this new species is the number of inner denticles (ID) found on the pedipalp fingers with six on the movable finger and usually five on the fixed finger, which more closely correlates with Vaejovis species from the mountains of southern Arizona rather than those geographically closer in northern Arizona.

The evolution of volcano-hosted geothermal systems based on deep wells from Karaha-Telaga Bodas, Indonesia

In late Mesozoic time, the southern Cordilleran foreland basin was bounded on the west by the Sevier thrust belt and on the south by the Mogollon highlands. Paleocurrent indicators in fluvial and fluviodeltaic strata imply sediment delivery into the basin from both tectonic features. Ages of detrital zircons in sandstones of the basin provide insights into the nature of the sediment sources. Upper Jurassic and Lower Cretaceous fluvial strata were deposited as sediment blankets across the width of the basin but Upper Cretaceous marginal-marine facies were restricted to the basin margin, with marine facies in the basin interior. Most Upper Jurassic and Lower Cretaceous fluvial sandstones contain heterogeneous age populations of Precambrian and Paleozoic detrital zircons largely recycled from Jurassic eolianites uplifted within the Sevier thrust belt or antecedent highlands, and exposed as sedimentary cover over the Mogollon highlands, with only minor contributions of Mesozoic zircon grains from the Cordilleran magmatic arc along the continental margin. Sources in Yavapai-Mazatzal Proterozoic basement intruded by anorogenic Mesoproterozoic plutons along the Mogollon highlands were significant for the Westwater Canyon Member of the Upper Jurassic Morrison Formation and for early Upper Cretaceous (Turonian) fluviodeltaic depositional systems, in which arc-derived Cordilleran zircon grains are more abundant than in older and younger units composed dominantly of recycled detritus. Detrital zircons confirm that the Salt Wash and Westwater Canyon Members of the Morrison Formation formed separate foreland megafans of different provenance. Late Upper Cretaceous (Campanian) fluvial sandstones include units containing mostly recycled sand lacking arc-derived grains in the Sevier foredeep adjacent to the Sevier thrust front, and units derived from both Yavapai-Mazatzal basement and the Cordilleran arc farther east, with some mingling of sand from both sources at selected horizons within the Sevier foredeep. Evidence for longitudinal as well as transverse delivery of sediment to the foreland basin shows that paleogeographic and isostatic analyses of thrust-belt erosion, sediment loads, and basin subsidence in foreland systems need to allow for derivation of foreland sediment in significant volumes from sources lying outside adjacent thrust belts.

RUDD CREEK PUEBLO: A LATE TULAROSA PHASE VILLAGE IN EAST CENTRAL ARIZONA

Rudd Creek Pueblo is a late Tularosa phase (A.D. 1225-1300) village located in the Upper Little Colorado region south of Springerville, Arizona. In 1996, Arizona State University, in cooperation with the Arizona Game and Fish Department, conducted archaeological fieldwork at Rudd Creek. This paper summarizes the results of that field season, which included the clearing of disturbed fill from a number of looted rooms, as well as limited test excavations in two great kivas, undisturbed rooms, and extramural areas. Comparison of the archaeology of Rudd Creek Pueblo with other Tularosa phase settlements in the Mogollon highlands along the Arizona-New Mexico border highlights key dimensions of variability in thirteenth century settlement in this area. Our investigations suggest that future research focusing on Tularosa phase settlements has the potential to contribute greatly to current debates in Southwest archaeology concerning migration, exchange, and population aggregation.

The Transition from the Preceramic to Ceramic Period in the Mogollon Highlands of Western New Mexico

The Transition from the Preceramic to Ceramic Period in the Mogollon Highlands of Western New Mexico