Geology and mineral deposits of the Mount Morrison quadrangle, Sierra Nevada, California

Abstract

The l\iount Morrison quadrangle includes part of the east front of the Sierra Nevada in Mono and Fresno Counties, Calif., ancl lies midway between Mono Lake on the north and Bishop on the south. The Sierra Nevada, characterized by alpine topography, occupies the southern half of the quadrangle and is separated from an area of relatively gentle topography to -the north by a steep ea~Stward-trending escarpment 2,500 to more than 8,000 feet high. Altitudes in the quadrangle range from less than 6,800 to more than 18,100 feet. The geologic units. mapped can be grouped into metasedimentary rod:s of Paleozoic age, metavolcanic rocks of Mesozoic nge, and intrusive rocks of Cretaceous age, which occur chietly in the Sierra Nevada, and extrusive and sedimentary rocks of Cenozoic age, which occupy the area north of the Sierra.The two groups of metamorphic rocks compose the Mount Morrison roof pendant, which underlies 42 square miles in the Sierrn Nevada and consists of a grossly homoclinal sequence of beds a little less than 50,000 feet thick. .The beds strike northwestward and dip steeply, with tops to the west. The common mineral assemblages of the rocks are typical of• the hornblende hornfels metamorphic facies of Turner and consist of quartz, mica, and feldspar in the more aluminous rocks and diopside, tremolite or actinolite, grossularite, and locally, wollastonite In the more calcareous varieties.The metasedimentary rocks of Paleozoic age compOEle the eastern three-fourths of the pendant. They are divided into 27 cartographic units, totaling 82,400 feet in maximum stratigraphic thickness, that range in age from Early Ordovician to Permian ( ?) . The rocks are divided into three blocks by two major fnults which strike almost parallel to the beds. The easternmost block contains six formations, with an approximate total thickness of 8,200 feet. The common rocks in this block are thin-bedded siliceous and pelitic hornfels, marble, slate, metachert, and a lesser amount of thin-bedded siliceous calc-hornfels and• thick-bedded calcareous quartz sandstone. Graptolites of Early Ordovician (Arenig) and Middle Ordovic\an (Caradoc) ages were found at several localities. The middle block comprises 10 formations with a total thiclmess of about 16,900 feet. The lower half of this block consists. chietly of thin-bedded 1 siliceous •and pelitic hornfels, slate, siliceous calc-hornfels, and marble: the upper half con-•Sis.ts of alternate thin-bedded siliceous hornfels and thickbedded calcareous quartz sandstone. Graptolites of Middle Ordovician (Caradoc) age were collected from the lower half, and one poorly preserved graptolite that may be as young as Silurian('!) was collected •near the top The westernmost block comprises five formations totaling 7,300 feet in thickness. Th~ lowest third of the block consists largely of thin-bedded siliceous hornfels and metachert but includes one distinctive PETROGRAPHY About 90 thin sections of the metasedimentary. rocks were examined with a petrographic microscope, and :~ ' .•. ', . .

Tomographic image of a seismically active volcano: Mammoth Mountain, California

“…A comprehensive description of the geology and geologic history of Mammoth Mountain is provided by Hildreth et al []. In their paper, Hildreth et al [] build upon the efforts of regional geologic mapping [ Rinehart and Ross , ; Huber and Rinehart , ; Bailey , ; Greene and Stevens , ] and geochronological studies [ Bailey et al , ; Mankinen et al , ; Mahood et al , ] to describe the regional setting and detailed geology of Mammoth Mountain. Several key points from the work of Hildreth et al [] that directly affect the derivation of the structural velocity models (section 5) are discussed below.…”

The Mississippian and Pennsylvanian (Carboniferous) systems in the United States

“…The Mount Baldwin Marble in the Mount Morrison pendant in the Sierra Nevada (loc. 25) has yielded probable Early Pennsylvanian fossils (Rinehart and Ross, 1964), so it evidently is coeval with the lower part of the Keeler Canyon Formation. The underlying clastic unit may correlate with some of the siliceous clastic rocks in the Perdido Formation-Rest Spring Shale sequence in the lnyo Mountains.…”

“…12, loc. 2), mapped and described by Rinehart and Ross (1964), contains more abundant and better preserved fossils than any other pendant in the eastern Sierra Nevada (Rinehart and others, 1959). The basal Carboniferous unit, the Bright Dot Formation (about 700 m thick) of Pennsylvanian ( ?)…”

“…Bloody Mountain Formation, is faulted against Triassic or Jurassic metavolcanic rock on the west side. Rinehart and Ross (1964) mapped tight northwest-trending folds in the Carboniferous rocks, and Russell and Nokleberg (1977), in their structural analysis, desc.rihed two deformations in the Carboniferous rocks. The first and dominant deformation resulted in upright folds whose axes plunge subhorizontally in vertical axial surfaces striking about N. 20° W. The second deformation resulted in minor upright folds.…”

Geological Survey research 1968, Chapter B

“…Quartzite is a well-known component of the Ordovician System in the Cordilleran miogeosyncline, where it composes large parts of the following formations: Eureka Quartzite (Hague, 1883;IGrk, 1933;Webb, 1958 ;Nolan and others, 1956), Swan Peak Quartzite (Richardson, 1913;R. J. Ross, Jr., 1951), Kinnikinic Quartzite (C. P. Ross, 1934Ross, , 1937, Toquima Formation (Ferguson, 1924), Convict Lake Formation (Rinehart and Ross, 1964), Johnson Spring Formation , W onah Quartzite (Walcott, 1924), and Mt. Wilson Quartzite (Norford, 1966).…”