Colorado Plateau Province Research Articles

Aeromagnetics and the Transition Between the Colorado Plateau and Basin Range Provinces

An aeromagnetic survey of central Utah has given improved resolution of a regional anomaly previously recognized from satellite magnetometer data. The anomaly consists of a gradient from a high over the Colorado Plateau to a low over the Basin Range province. Magnetic profiles are fit by a model in which the Curie isotherm deepens eastward in a belt up to 80 km wide, whose western side is about 50 km east of the Basin Range physiographic margin. The magnetic profiles could also be fit be a change of average crustal susceptibility instead of Curie depth. In either case we conclude that the major lateral change between Basin Range and Colorado Plateau crustal geophysical parameters occurs not at the Fenneman physiographic boundary but more than 50 km eastward of it. This suggestion is found to be consistent with data from seismic refraction, geomagnetic variation, geochemistry, and geologic structures.

Stratigraphic Analysis of Upper Permian and Lower Triassic Strata in Southern Utah

Permian sedimentation in southwestern Utah was influenced by three principal depositional areas--the Oquirrh basin in north-central Utah, the Cordilleran geosyncline in eastern Nevada, and the Quemado-Cuchillo basin on the northern shelf of the Sonoran geosyncline in east-central Arizona and west-central New Mexico. Throughout Permian time, marine sediments and well-developed beach and continental eolian sandstone equivalents were deposited within these basins and on the surrounding shelves. Each of the three depositional sites appears to have exerted influence on sedimentation during a discrete period of geologic time. Thus, while one basin was the site of sedimentation, the other two basins were relatively quiescent. Remarkably similar beach and continental sandstone deposits are related to each basin, and all these sandstones extend to a common depositional area in southwest Utah where they are interlayered. Vertical juxtaposition or interlayering of littoral and beach sandstone facies that are related to three differing sedimentational basins has been responsible for most of the problems invo ving Permian nomenclature and correlation in the Colorado Plateau province. Stratigraphic analyses show that each continental sandstone facies has a basinal stratigraphic equivalent which consists primarily of interbedded carbonate with smaller amounts of sandstone and shale. The beach and basinal equivalents present are: Cedar Mesa Sandstone equivalent to Elephant Canyon carbonates; Organ Rock Shale equivalent to Meseta Blanca Sandstone and Yeso evaporites and carbonates; Coconino Sandstone, to upper De Chelly Sandstone; White Rim Sandstone (approximately upper 80 percent), to Toroweap Formation; and upper White Rim Sandstone, to lowermost (Gamma member) Kaibab Formation. Rock units underlying the Toroweap-White Rim Formations are younger toward the south. The Kaibab Formation is a stratigraphic continuation of the Franson Member of the Park City Formation in northern Utah and southwestern Wyoming and is inferred to be time-transgressive. The Permian-Triassic boundary is recorded by a pronounced unconformity in southwesternmost Utah. Northward, the break is less pronounced and is not recognizable in north-central Utah. Early Triassic sedimentation in southern Utah appears to record cyclic response to one major subsiding sedimentational area, the Cordilleran Triassic basin, apparently with characteristic onlap relations, and at least two and possibly three of the Early Triassic Moenkopi units are not present at the Moenkopi type section in northern Arizona. The southward continuation of the Woodside Formation from southwestern Wyoming to central Utah is now recognized. The Sinbad and Timpoweap Members of the Moenkopi Formation are shown to be the same stratigraphic unit. Subsurface control suggests that the Virgin Limestone Member extends into central Utah. Structurally, most of southern Utah appears to have been a slowly subsiding shelf throughout most of Permian and Early Triassic times.

A Study of Wolf Spider Ecology in Grand County, Utah (Lycosidae: Araneae)

The author correlates the results of a twenty-one day pitfall trap program, where wolf spiders were trapped from the various habitats of the Moab area, Utah. Species partitioning land biotic associations are discussed for the six species found in the study area. A seemingly habitat restricted color variation of Pardosa sternalis (Thorell) is described. This report summarizes the results of a twenty-one day trapping program and correlates the biotic associations and relative abundance of ground dwelling wolf spiders of the desert floor. No prior studies have been reported on the spiders which live on the desert floor. Chew (1961) dealt solely with the spiders associated with the vegetation of the desert shrub community. The study area included the Arches National Monument near Moab, Utah, and the nearby Canyonlands National Park. The trapping period was from 15 June to 15 July, 1966. The Moab area, with elevation of 4,042 feet, is part of the Colorado plateau Province; it has an annual average temperature of 54.1 degrees Fahrenheit and an annual temperature range of -24 to 111 degrees Fahrenheit. The average annual precipitation is 9.52 inches, including an annual snowfall of 16.5 inches.' The region is subject to great fluctuation and extreme variation in both temperature and rainfall between the various seasons of the year. The summers are hot and dry with cool nights, while the winter is cold and windy. Most of the pre- cipitation falls as snow in January to May. June and July are the dry periods. HABITATS OF THE STUDY AREA. Six habitats are recognized in this portion of the Colorade Plateau Province: Rock Formations, Pinyon-Juniper Woodland, the Desert Shrub Community, the Washes, 1 Climatic Summary of the United States (U.S. Weather Bureau, section 21).

New Developments on Age and Extent of Ouray Limestone

The Ouray limestone extends from the surface in the San Juan Mountains of Colorado into the subsurface of much of the Colorado Plateau Province. Previous lithologic correlations have been verified by a study of the fauna of a cored interval in the Shell Oil Company-Continental Oil Company's Hovenweep No. 1, San Juan County, Utah. This fauna contains Paurorhyncha sp. and Cyrtospirifer whitneyi cf. animasensis, verifying the lithologic and mechanical log correlation with the Ouray limestone outcrops. Inasmuch as the typical Ouray limestone fauna has both Mississippian and Devonian aspects and the formation contacts are gradational, the writers suggest that the unit is transitional between the Upper Devonian, Elbert formation and the Lower Mississippian, Leadville limestone.

GEOLOGY OF THE UINKARET PLATEAU, NORTHERN ARIZONA

The Uinkaret Plateau, a major block of the Colorado Plateau province in northern Arizona, is bounded on the west by the Hurricane Ledge, developed along the Hurricane fault, and on the east by scarps developed along the Toroweap and Sevier faults. Over the southern part there are extensive outpourings of lava which fall into four age groups. The oldest eruptions preceded earliest movement along the Hurricane fault and antedated cutting of the present Grand Cayon. These lavas poured out on a relatively even surface believed to have been a large pediment or series of pediments extending at least 16 miles north from the Colorado River. Extensive dissection of the oldest lavas preceded the next eruptions, which took place at considerably lower elevations. The Inner Gorge of Grand Canyon was cut to approximately its present depth and later filled to a height of at least 600 feet and perhaps 1,200 by lava floods from Toroweap Valley. The lava dams were entirely removed before later flows, pouring into the Inner Gorge from the rim of the Esplanade, again dammed the river, which has removed all but small portions of these dams. Repeated movements along the Toroweap fault have occurred in post-lowan-Wisconsin time. In the very recent past, renewed volcanic activity formed a single small cone and lava flow.

Geographic and geologic sketch of the Capitol Reef region, Utah

The Capitol Reef region which includes the recently established Capitol Reef National Monument exhibits in general the stratigraphic, structural, and physiographic features of the Colorado Plateau Province. In the canyons of Fremont River all the Triassic and Jurassic formations elsewhere exposed in southern Utah, likewise the displacements caused by the Water Pocket Fold and the Thousand Lake fault, are well displayed. Special local features are the thinness of the Chinle and Shinarump, the presence of much sandstone and limestone in lower Triassic beds heretofore classed as Carboniferous, the unusual composition of the San Rafael group, and the extensive surfaces of erosion about 300 feet above present drainage channels.

The Toreva-Block: A Distinctive Landslide Type

An end member of the "rock-slide" group is described and named from an assigned type locality in the Hopi Indian Reservation of northeastern Arizona. A Toreva-block consists essentially of an unbroken tilted mass of stratified material which in numerous instances measures over 1,000 feet along the strike. Attempt is made to relate the slides to pediment remnants at the type locality. Distribution and character of Toreva-blpcks elsewhere in the Colorado Plateau Province are briefly discussed. Available data suggest the late Pleistocene formation of the larger slides.

Epicycles of Erosion in the Valleys of the Colorado Plateau Province

The results of physiographic and historical studies of recent channeling in previously well-aggraded valleys in the Colorado Plateau Province are here presented. Discussion is given to the unconformities and alluvial terraces in the valley fills, evidences of other epicycles of erosion. Studies were made of naturally barren areas to determine if there had been a change in the gradational processes, which would be expected if climate had changed sufficiently to cause the accelerated erosion in adjacent valleys. Conclusions are that utilization of the region by man and the consequent reduction and modification in the plant cover are major factors in starting the new epicycle of erosion.

A Study in the Colorado Plateau Province

A Study in the Colorado Plateau Province

The Colorado Plateau province as a field for geological study

The Colorado Plateau province as a field for geological study

Scientific Serials

American Journal of Science and Arts, July.—Prof. Loomis here gives some interesting results obtained from observations of the United States Signal Service. Whenever an area of low barometer is formed in the United States, there seems to be always an area of high barometer about 1,200 miles to the south-east. The same thing was found to hold for the Atlantic Ocean and Europe, the average distance between the areas being here 1,700 miles, and the direction rather more southerly. Areas of high pressure are probably formed from air that is expelled from those of low. Low barometer is generally associated with high temperature, so we might conclude that a temperature above the mean in Iceland would be accompanied by one below the mean in Central Europe; this was verified. An unusually high barometer in Central North America may be the result of storms 1,500 or 2,000 miles to the north-west. Prof. Loomis found the average forms of the isobars about an area of maximum pressure, an oval with major axis nearly double the minor. The forms about minima were nearly the same; as were also the directions of the major axes in both cases (N.E). The rainfall is least when the pressure at the centre of a storm is increasing (or the storm diminishing in intensity), greatest in the opposite case. The stationariness for several days of storms near Nova Scotia or Newfoundland, seems due to unusual rainfall there. Prof. Loomis lastly furnishes data as to the course and velocity of storms in tropical regions.—Prof. Farlow has studied a disease which caused much loss of olive and orange crops in California last summer. He says that though first attracting the eye by the presence of a black fungus, the disease is not caused by it, but rather by the attack of some insect, which deposits some gummy substance on the leaves and bark, or so wounds the tree as to cause some sticky exudation on which the fungus especially thrives. The fungus greatly aggravates the trouble, but in seeking a remedy, it is necessary to look further back.—Mr. Gilbert gives a description of the Colorado Plateau Province as a field for geological study; it offers valuable matter in an advantageous manner.—Drs. Blake and Genth describe a vanadium mica found on the western slope of the Sierra Nevada, and to which the name of Roscoelite is given, in honour of Prof. Roscoe. It contains quite a large per-centage of vanadium (20.16), which is present as V6O11. This mica is found in the hanging wall of a small quartz vein, the country rock being porphyry ; fine scales of gold occur between the crystals.—We may further mention a series of notices of recent American earthquakes (1874—76), by Prof. Rockwood. —Mr. Grinnell describes, in the Appendix, a Crinoid from the Cretaceous formation of the West.

The Colorado plateau province as a field for geological study

The Colorado plateau province as a field for geological study