Western Sierra Nevada Foothills Research Articles

Climatic influences on survival and reproductive transitions of big-eared woodrats in California oak woodland

AbstractIt is known that climatic factors can influence the reproductive performance of small mammal populations. However, this information has not been available for the big-eared woodrat (Neotoma macrotis), a keystone species that inhabits the California central coast ranges south to Mexico and the oak woodlands (Quercus spp.) of the western Sierra Nevada foothills. From 2002 to 2014, we livetrapped woodrats on 1.1-ha study plots in coastal-central California and recorded their age and reproductive status. We analyzed these data by a capture-mark-recapture (CMR) framework to estimate state-specific recapture probability (p) and monthly apparent survival (S) of juvenile, non-reproductive, and reproductive adult female woodrats, and the influence of rain and temperature on S and transition probability (Ψ) of the three states. Rainfall from the previous season did not markedly affect survival rates of the states, with one exception: it decreased the survival of nonreproductive woodrats. Nearly all breeding occurred during the cool, wet winter season. Juvenile woodrats had at least a 0.55 probability of breeding by their first winter, conditional on survival. Temperature during the breeding season had a marked negative influence on transition probability. During winter, survival of nonreproductive adult females was significantly higher than for juvenile and reproductive females, indicating a cost of reproduction. Physiological effects and diminished diet quality due to further climate warming could reduce the reproductive success of female big-eared woodrats with negative consequences on population growth and persistence.

Modeling Climate Suitability of the Western Blacklegged Tick in California.

Ixodes pacificus Cooley & Kohls (Acari: Ixodidae), the primary vector of Lyme disease spirochetes to humans in the far-western United States, is broadly distributed across Pacific Coast states, but its distribution is not uniform within this large, ecologically diverse region. To identify areas of suitable habitat, we assembled records of locations throughout California where two or more I. pacificus were collected from vegetation from 1980 to 2014. We then employed ensemble species distribution modeling to identify suitable climatic conditions for the tick and restricted the results to land cover classes where these ticks are typically encountered (i.e., forest, grass, scrub-shrub, riparian). Cold-season temperature and rainfall are particularly important abiotic drivers of suitability, explaining between 50 and 99% of the spatial variability across California among models. The likelihood of an area being classified as suitable increases steadily with increasing temperatures >0°C during the coldest quarter of the year, and further increases when precipitation amounts range from 400 to 800 mm during the coldest quarter, indicating that areas in California with relatively warm and wet winters typically are most suitable for I. pacificus. Other consistent predictors of suitability include increasing autumn humidity, temperatures in the warmest month between 23 and 33°C, and low-temperature variability throughout the year. The resultant climatic suitability maps indicate that coastal California, especially the northern coast, and the western Sierra Nevada foothills have the highest probability of I. pacificus presence.

Terranes of the Western Sierra Nevada Foothills Metamorphic Belt, California: A Critical Review

Previous classifications of the western Sierra Nevada Foothills belt have been modified into five geologic packages: the Northern Sierra terrane, Feather River terrane, Calaveras Complex, Jura-Triassic arc belt, and Middle—Late Jurassic arc sequence. The Northern Sierra terrane comprises the Shoo Fly Complex and an overlying Paleozoic succession of arc volcanics. The Feather River terrane is predominantly serpentinized ultramafics containing tectonic blocks of amphibolite, plagiogranite, and mafic schists. The Permian-Late Triassic Calaveras Complex is a subduction mélange comprising psuedostratigraphic sequences of both chert and argillite with incorporated blocks of limestone, amphibolite, greenschist, phyllite, and basalt. The Red Ant schist is also included in this terrane even though it is of higher metamorphic grade. The Jura-Triassic arc belt consists of a Paleozoic basement of disrupted ophiolite, serpentinite mélange, and ultramafic rocks overlain by uppermost Triassic—Early Jurassic arc volcanics and coeval 200 Ma intrusive rocks. This belt may comprise several small terranes. The Middle—Late Jurassic arc sequence comprises 165-155 Ma volcanic arc rocks, greenstones, and metasedimentary rocks of the Mariposa Formation, and rocks of the Smartville Complex. Coeval intrusive rocks are included within this sequence because they are probably comagmatic with the arc volcanics. The Northern Sierra terrane and Feather River terrane are bounded by pre-Nevadan structures that may represent original sutures or subduction zones and have geologic histories that are relatively decoupled from adjacent rocks; they are therefore designated as terranes. The Calaveras Complex formed either adjacent to the Cordilleran margin as a result of east-dipping subduction, adjacent to arc rocks of the Jura-Triassic arc belt from west-dipping subduction, or a combination thereof. Therefore, the Calaveras Complex has a common geologic history with adjacent rocks and is not designated as a terrane. The Jura-Triassic arc belt comprises several ophiolitic microterranes, which may have been either exotic or fringing relative to North America, and are therefore grouped as a belt instead of individual terranes. The Middle-Late Jurassic arc sequence unconformably overlies rocks of the Jura-Triassic arc belt and is therefore a cover sequence instead of a separate terrane. The accretionary history of the Mesozoic Cordilleran margin is complex. After emplacement of the Northern Sierra terrane and Feather River terrane, the system was dominated by arc volcanism and accretion. The entire Sierra Nevada Foothills metamorphic belt was likely accreted to the margin by the Late Jurassic. The Sierra Nevada Foothills comprise units that appear to be correlative with those in the Klamath Mountains. Possible correlations are drawn between the Northern Sierra terrane and Eastern Klamath terrane, Calaveras Complex + Red Ant Schist and Stuart Fork + Eastern Hayfork terranes, Jura-Triassic arc belt and Rattlesnake Creek terrane, and Middle-Late Jurassic arc sequence and Western Hayfork terrane + coeval intrusives.

Seasonal and event-scale variations in solute chemistry for four Sierra Nevada catchments

Hydrobiogeochemical processes controlling stream water chemistry were examined in four small (<5 km 2) catchments having contrasting bedrock lithologies in the western Sierra Nevada foothills of California. The Mediterranean climate with its cool/wet and hot/dry cycle produces strong seasonal patterns in hydrological, biological and geochemical processes. Stream water solutes fall into three general groups according to seasonal fluctuation in concentration: strong, rainy season minimum–dry season maximum (Cl −, SO 4 2−, base cations); weak, rainy season minimum–dry season maximum (Si); and rainy season maximum–dry season minimum (NO 3 − and K +). Solute dynamics in soil solutions and stream water suggest that mixing of drainage waters from bedrock and soil sources regulate stream water solute concentrations. Patterns are further altered by the leaching of solutes accumulated in the soil over the summer period of desiccation and the temporal discoupling of nutrient cycles that occurs due to differences in the timing between vegetation growth (late spring) and leaching (early winter). Solute concentrations are remarkably similar between watersheds with varying bedrock types, with the exception of nitrate, sulfate and bicarbonate. Three watersheds have nitrogen-bearing metasedimentary bedrock that contributes to elevated nitrate concentrations in stream waters. Watersheds whose bedrock includes mineralized veins of sulfide and carbonate minerals similarly have greater sulfate and bicarbonate concentrations in stream water. Hydrobiogeochemical processes are highly dynamic at the seasonal and storm-event temporal scales and spatially complex at the watershed scale making management of stream water chemical composition, such as nitrate concentrations, very challenging.

Ecology of Borrelia burgdorferi in ticks (Acari: Ixodidae), rodents, and birds in the Sierra Nevada foothills, Placer County, California.

This study examined the prevalence of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner in host-seeking adult and nymphal Ixodes pacificus Cooley & Kohls and estimated the I. pacificus infestation and B. burgdorferi infection of rodent and avian hosts in the western Sierra Nevada foothills of northern California. Additionally, we identified species likely to participate in an enzootic cycle for B. burgdorferi in this yellow pine transition habitat. Evidence of infection with B. burgdorferi was identified in 7.3 and 5.4% of host-seeking I. pacificus adults and nymphs, respectively. Mean numbers of I. pacificus observed on rodents were 1.15 for Neotoma fuscipes Baird and 0.18 for Peromyscus spp. One of 104 ear punch tissues obtained from woodrats and none from 49 Peromyscus spp. yielded B. burgdorferi. A total of 291 collected birds representing 34 species had a mean of 0.27 I. pacificus per bird. The mean I. pacificus infestation of ground-dwelling birds was 2.5 ticks per bird. Forty-nine of 92 (53%) blood smears collected from birds were reactive to a B. burgdorferi specific antibody. This study presents the identification of a B. burgdorferi-like spirochete in birds in western North America. The tick burden and spirochete infection of birds suggests that birds may be involved in a local B. burgdorferi enzootic cycle and likely participate in the transport of ticks and spirochetes to other locations while rodents from this site do not appear to be major contributors.

Economic Relationships of Brushpiles, Forage Production, and California Quail Hunting

Harvesting trees for firewood in the oak hardwood rangelands of the western Sierra Nevada foothills creates slash that may be burned to improve livestock forage production or piled into brushpiles for wildlife. The economics of these actions are undocumented. We observed a firewood harvest that created 378 brushpiles averaging 13.6 m2 and 1.3 m high, and resulted in a forage loss of 1,807 kg dry weight, equivalent to 4.4 AUM. We projected the present net value of 5 management options concerning the removal or retention of brushpiles during a 15-year period. Inputs included revegetation of burned-brushpile sites, annual forage production on areas with the oak canopy removed, burning and reseeding costs, and income derived from cattle grazing and quail hunting. The options were: (A) burning all brushpiles and reseeding the burned sites; (B) option A without reseeding; (C) burning 235 brushpiles and reseeding, leaving 23 brushpiles/ha for quail; (D) option C without reseeding; (E) leaving all brushpiles. All but option B were economically feasible at a 4% interest rate; at an 8% interest rate, only options C-E were profitable. After 15 years, the accumulated returns per hectare at 4% for options A-E were $11.67, $-3.97, $32.43, $22.29, and $23.35, respectively, and at 8%, $-17.35, $-25.74, $8.58, $3.02, and $17.98, respectively.

Estimated thickness of granitoid rocks in the western Sierra Nevada foothills near Oakhurst, California: A hydrogeological approach

Research Article| December 01, 1987 Estimated thickness of granitoid rocks in the western Sierra Nevada foothills near Oakhurst, California: A hydrogeological approach SEYMOUR MACK SEYMOUR MACK 1Geology Department, California State University, Fresno, California 93740 Search for other works by this author on: GSW Google Scholar Author and Article Information SEYMOUR MACK 1Geology Department, California State University, Fresno, California 93740 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 99 (6): 880–885. https://doi.org/10.1130/0016-7606(1987)99<880:ETOGRI>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation SEYMOUR MACK; Estimated thickness of granitoid rocks in the western Sierra Nevada foothills near Oakhurst, California: A hydrogeological approach. GSA Bulletin 1987;; 99 (6): 880–885. doi: https://doi.org/10.1130/0016-7606(1987)99<880:ETOGRI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract East of the Oakhurst and Fine Gold metamorphic belts in the western Sierra Nevada foothills, saline water is believed to be leaking upward from an eastward-dipping fault which is truncated at depth by a carapace of granitoid rock. Saline water draining from the Sierran block is presumed to have migrated westward through metamorphic basement ultimately to rise along the buried fault, which appears to be the southeastward continuation of the Melones fault. Wells yielding the sodium chloride-rich water lie along a N30°W, 100-km-long trend referred to as the “Foothill lineament,” which lies east of, and subparallel to, the surface expression of the Melones. Estimates of thickness of the granitoid capping in the vicinity of Oakhurst and Fine Gold are obtained by applying the angle of dip of the Melones fault and the horizontal distance between the Melones and the saline lineament. Data from the Fine Gold metamorphic bell appear to be the most reliable because the average angle of dip (62° east) is reasonably consistent throughout the shear units comprising the fault zone. Calculated thickness along the saline lineament near Fine Gold ranges from 9.2 to 10.3 km for eastern and western shear zones and 9.7 km for the median position between shear units. These values show a startling correlation with an estimate of granitoid thickness of 9.8 km in the western foothills on the basis of data obtained from a northeast-southwest refraction seismic transect through the Sierra Nevada by Bateman and Eaton. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fossil Plethodontid Salamanders from the Latest Miocene of California

Two salamanders, Aneides lugubris, and Batrachoseps sp., are reported from the latest Miocene (Hemphillian) upper Mehrten Formation of the western Sierra Nevada foothills of California. A record of Batrachoseps sp. is also reported here from the Pinole Tuff of the same age in the San Francisco Bay area of California. These are the second Tertiary records of plethodontid remains and the first from west of the Rocky Mountains. The minimum age of Aneides lugubris, and the Sierra Nevada population in particular, is established at approximately five million years. This is consistent with the estimated longevity of this species based on biochemical evidence and modifies a previous biogeographic speculation. Prior to Peabody's (1959) description of late Miocene trackways of Batracho- seps from near Columbia, California, the fossil record of plethodontid salaman- ders did not extend earlier than the Pleistocene. Since then there has been only one unquestionable plethodontid record from rocks older than the Pleis- tocene-four vertebrae from the early

Hydrogeology of the Sierra Nevada Foothill Lineament Near Oakhurst, California

ABSTRACTThirty‐three wells and two springs yielding high chloride water from granitic rocks define a northwesttrending lineament, which extends for 60 miles (100 km) along the western Sierra Nevada foothills of Fresno and Madera Counties. Geochemical evidence indicates that many of the constituents in this water are marine connate in origin. However, the connate water has been strongly diluted with meteoric water. The connate water is believed to have been derived from Paleozoic and early Mesozoic marine clastic rocks (now metamorphosed) in the Sierra Nevada. The lineament marks the location where marine connate water has migrated upward from these rocks along an eastward‐dipping fault zone. A capping of granitic rocks has enhanced the persistence of this connate water for millions of years. The lineament may be structurally related to the Oakhurst‐Fine Gold fault zone, which it parallels for approximately 15 miles (25 km). There is a remarkable correlation in the Oakhurst area between wells yielding high‐chloride water and fracture trends determined from aerial photographs. High chloride ground water is present only in topographically low areas, where little flushing by meteoric water has been possible.

Seismic Models of the Root of the Sierra Nevada

Seismic waves generated by earthquakes or explosions show a delay in travel times as they propagate across the Sierra Nevada from all directions except that of the Nevada test site. Early arriving waves from the test site can be explained if they emerge through a rock layer with high seismic velocity from the sharp eastern edge of the Sierran root. Such a layer could be formed by the subducted ophiolite slab that crops out in the western Sierra Nevada foothills. A synthesis of all seismic data indicates that the Sierran root projects downward into the mantle to a depth of about 55 kilometers beneath the high Sierra.

Geology of the Pine Hill Intrusive Complex, a Layered Gabbroic Body in the Western Sierra Nevada Foothills, California

The western Sierra Nevada metamorphic belt was subjected to several episodes of tectonism and metamorphism (Clark, 1960a, 1964; Baird, 1962; Bateman and others, 1963; Bateman and Wahrhaftig, 1966; Evernden and Kistler, 1970; Bateman and Clark, 1974; Schweickert and Cowan, 1975; Duffield and Sharp, 1975). The Foothills fault system (Clark, 1960b), which approximately parallels the regional strike of the metamorphic rocks, divides the metamorphic belt into a series of elongate structural blocks. The western Sierra Nevada metamorphic belt is intruded throughout its entire length by granitic, gabbroic, and ultramafic plutonic rocks. Ultramfic rock, which is largely serpentinized, occurs as conformable lenticular bodies which commonly coincide with major fault zones. Granitic rock which locally intrudes the ultramafic rock was emplaced mainly during the Inyo Mountains (180 to 160 m.y.) or Yosemite (148 to 132 m.y.) intrusive epochs (Evernden and Kistler, 1970). Gabbroic rock which occupies much less areal extent than either the granitic or ultramafic plutonic rocks has been genetically related to both the granitic and ultramafic rocks as well as to the enclosing metavolcanic rock (Durrell, 1940; Hietanen, 1951, 1976; Compton, 1955; Eric and others, 1955; Bateman and others, 1963; Clark, 1964; Putnam and Alfors, 1969; Olmsted, 1971). The purpose of this study is to investigate the structure, petrology, mineralogy, and chemistry of one of the largest gabbroic plutons in the western Sierra Nevada metamorphic belt, the Pine Hill intrusive complex. The origin and emplacement of this intrusion in relation to the evolution of the western metamorphic belt is also discussed. Geologic Setting East of Sacramento, California, the western Sierra Nevada metamorphic belt can be divided into at least four structural blocks, each separated by a major fault zone (Fig. 1). As most fault zones in the western Sierra Nevada metamorphic belt have been mapped on the occurrence of linear bodies of sheared serpentinite and/or highly schistose metamorphic rock and “do not systematically repeat or offset dated stratigraphic successions, the nature and amount of offset along the major fault zones” (Schweickert and Cowan, 1975) is generally unknown.

Geology of the Pine Hill intrusive complex, a layered gabbroic body in the western Sierra Nevada foothills, California: Summary

Geology of the Pine Hill intrusive complex, a layered gabbroic body in the western Sierra Nevada foothills, California: Summary

Origin and Emplacement of the Academy Pluton, Fresno County, California

The Academy Pluton is located in the western Sierra Nevada foothills northeast of Fresno, California (Fig. 1). It cuts the northern end of the Kings-Kaweah ophio-lite belt, which forms a 125-km-long northwest-trending zone of highly deformed mafic and ultramafic country rocks between the Kings and Tule Rivers of the foothills region (Saleeby, 1975, 1976a, 1976b). The Academy Pluton is one of a number of Jurassic and Early Cretaceous plutons which have intruded and metamorphosed the ophiolitic rocks; these crosscutting plutons form the western margin of the Sierra Nevada Batholith in the latitude of the Kings-Kaweah ophiolite belt. They range in composition from olivine-hornblende melagabbro to hornblende-biotite granodiorite, and many of then appear to have been preferentially emplaced into the structurally weakened zone provided by the disrupted ophiolite belt (Saleeby, 1975, 1976b). To the east, the main body of the Sierra Nevada Batholith is underlain primarily by more silicic middle to Late Cretaceous plutons which range in composition from granodiorite to granite. North of the Academy area, this compositional trend is found to exist all along the western Sierra Nevada foothills. The Guadalupe complex east of Merced (Best, 1963), the Pine Hill gabbro east of Sacramento (Springer, 1971), and the Bucks Lake Pluton (Hietanen, 1973) at the north end of the western metamorphic belt are representative of the more basic and older plutons comprising the western margin of the Sierra Nevada Batholith. The Academy Pluton is one of the most complexly zoned plutons in the western sierra Nevada. The earliest reference to the pluton was by Macdonald (1941), who described the pluton as being composed of hypersthene-bearing quartz diorite. His map (1941, P1.1) showed an indefinite contact between hypersthene-bearing quartz diorite and surrounding pyroxene-free quartz diorite and tonalite. The present investigation has established that pyroxene-free quartz diorite and tonalite lying peripherally to the morth and east of Macdonald's contact is part of the Academy Pluton but tonalite South of the pluton cuts across the Academy structure and thus represents a later magmatic esisode. In preliminary studies, the senior author of this paper noted that there were at least three, and possibly four, ring-like zones comprising the pluton and that the innermost zone was composed of more basic rock than the outermost zones. The difficulty in explaining the gradational contacts and the apparent reversed zoning in the pluton prompted this study.

Saline water in the foothill suture zone, Sierra Nevada Range, California

Research Article| July 01, 1979 Saline water in the foothill suture zone, Sierra Nevada Range, California SEYMOUR MACK; SEYMOUR MACK 1School of Natural Sciences, Department of Geology, California State University, Fresno, California 93740 Search for other works by this author on: GSW Google Scholar LORRAINE M. FERRELL LORRAINE M. FERRELL 1School of Natural Sciences, Department of Geology, California State University, Fresno, California 93740 Search for other works by this author on: GSW Google Scholar Author and Article Information SEYMOUR MACK 1School of Natural Sciences, Department of Geology, California State University, Fresno, California 93740 LORRAINE M. FERRELL 1School of Natural Sciences, Department of Geology, California State University, Fresno, California 93740 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1979) 90 (7): 666–675. https://doi.org/10.1130/0016-7606(1979)90<666:SWITFS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation SEYMOUR MACK, LORRAINE M. FERRELL; Saline water in the foothill suture zone, Sierra Nevada Range, California. GSA Bulletin 1979;; 90 (7): 666–675. doi: https://doi.org/10.1130/0016-7606(1979)90<666:SWITFS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Thirty-one wells yielding sodium chloride water and dissolved solids averaging 1,300 mg per liter have been drilled into granitic rocks of the western Sierra Nevada foothills of Fresno and Madera Counties, California. Their chemistry contrasts sharply with that of thousands of other wells tapping granitic rocks in the area which yield good quality bicarbonate water that is low in dissolved solids. The sodium chloride wells are along a N30°W, 85-km-long trend, herein referred to as the “foothill lineament.” The foothill lineament appears to be an extension of the foothill suture into the intervening granitic terrane between the Melones Fault on the north and the Kings-Kaweah suture on the south. Based on various chemical parameters such as B/Cl and Br/Cl, the sodium chloride waters appear to be marine connate in origin, albeit strongly diluted with meteoric water. Several hypotheses are advanced to explain why saline waters are concentrated along the foothill lineament, although all arguments have serious drawbacks. No matter how the sodium chloride waters have originated, the foothill lineament is believed to define a profound structural element, possibly contiguous with the early Mesozoic foothill subduction complex, along which these waters have migrated toward the surface. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Sulfide mineralogy of metamorphosed ultramafic rocks, western Sierra Nevada foothills, California

Sulfide mineralogy of metamorphosed ultramafic rocks, western Sierra Nevada foothills, California

Contact Metamorphosed Ultramafic Rocks in the Western Sierra Nevada Foothills, California

Within the western Sierra Nevada metamorphic belt, linear bodies of alpine-type ultramafic rock, now composed largely of serpentine minerals, parallel the regional strike and commonly coincide with major fault zones. Within this metamorphic belt, east of Sacramento, California, ultramafic rocks near a large mafic intrusion, the Pine Hill Intrusive Complex, have been emplaced during at least two separate episodes. Those ultramafic rocks, evidently unaffected by the Pine Hill Intrusive Complex and composed largely of serpentine minerals, were emplaced along a major fault zone after emplacement of the Pine Hill Intrusive Complex. Those ultramafic rocks, contact metamorphosed by the Pine Hill Intrusive Complex, show a zonation of mineral assemblages as the igneous contact is approached: olivine+antigorite+chlorite +tremolite+Fe-Cr spinel↑ olivine+talc+chlorite+tremolite+Fe-Cr spinel ↑ olivine+anthophyllite+chlorite+tremolite+Fe-Cr spinel ↑ olivine+orthopyroxene+aluminous spinel+hornblende+Fe-Cr spinel. Superimposed on these mineral assemblages are abundant secondary minerals (serpentine minerals, talc, chlorite, magnetite) which formed after contact metamorphism. Correlation of observed mineral assemblages with the experimental systems, MgO-SiO2-H2O and MgO-Al2O3-SiO2-H2O suggests an initial contact temperature of 775±25 °C for the Pine Hill Intrusive Complex assuming Ptotal ≃Pfluid ≃PH2O. The pressure acting on the metamorphic rock during emplacement of the intrusion is estimated to be a minimum of 1.5 kb.