DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP MF-1559-A UNITED STATES GEOLOGICAL SURVEY MINERAL RESOURCE POTENTIAL OF PART OF THE VENTANA WILDERNESS AND THE BLACK BUTTE, BEAR MOUNTAIN, AND BEAR CANYON ROADLESS AREAS, MONTEREY COUNTY, CALIFORNIA SUMMARY REPORT By V. M. Seiders U.S. Geological Survey and L. E. Esparza, Charles Sabine, J. M. Spear, Scott Stebbins, and J. R. Benham U.S. Bureau of Mines STUDIES RELATED TO WILDERNESS Under the provisions of the Wilderness Act (Public Law 88-577, September 3, 1964) and related acts, the U.S. Geological Survey and the U.S. Bureau of Mines have been conducting mineral surveys of wilderness and primitive areas. Areas officially designated as "wilderness," "wild," or "canoe" when the act was passed were incorporated into the National Wilderness Preser­ vation System, and some of them are presently being studied. The act provided that areas under consideration for wilderness designation should be studied for suitability for incorporation into the Wilderness System. The mineral surveys constitute one aspect of the suitability studies. The act directs that the results of such surveys are to be made available to the public and be submitted to the President and the Congress. This report discusses the results of a mineral survey of part of the Ventana Wilder­ ness and the Black Butte (5102), Bear Mountain (5103), and Bear Canyon (5104) Roadless Areas, Los Padres National Forest, Monterey County, California. The Ventana Wilderness was established by Public Law 91-58; this report discusses additions to the Ventana Wilderness that were established by Public Law 95-237 in 1978. The Black Butte, Bear Mountain, and Bear Canyon Roadless Areas were classified as further planning areas during the Second Roadless Area Review and Evaluation (RARE II) by the U.S. Forest Service, January 1979. SUMMARY A geologic, geochemical, and geophysical investigation and a survey of claims and prospects have been conducted to eval­ uate the mineral resource potential of part of the Ventana Wilderness and the Black Butte, Bear Mountain, and Bear Canyon Roadless Areas. The study area is part of the Los Padres National Forest and lies in the Santa Lucia Range on the central Cali­ fornia coast. Most of the area is underlain by crystalline basement consisting of high-grade metamorphic rocks intruded by Creta­ ceous granitic plutons which is unconformably overlain by sedimentary rocks of Late Cretaceous and Tertiary age. There has been virtually no mining within the study area. In the central California coastal area, most mining of metallic- mineral deposits has been from rocks of the Franciscan assemblage; igneous and metamorphic rocks like those of the study area have yielded no significant deposits. Geochemical study of 167 stream-sediment samples showed anomalous values of certain elements in 9 samples, but most of these anomalies appear to correlate with minerals that are not abundant enough to indicate resource potential. Field examination and chemical analyses of rock samples revealed little evidence of metallic mineralization. The igneous and metamorphic rocks of the study area have a low potential for metallic-mineral deposits and no potential for oil and gas. Petroleum and natural gas are produced from sandstone in the Monterey Formation in the nearby Salinas Valley. The Monterey in the study area is beyond the known limits of productive sandstone and has a low potential for oil and gas production. Other sedimentary rocks of the area have a very low potential for oil and gas. The sedimentary rocks have a low or no potential for metallic-mineral deposits. The Monterey Formation contains phosphate rock in the study area, but the abundance is not known; there may be a low resource potential. The study area contains deposits of crystalline limestone, sand, and gravel. The deposits are small and inaccessible and thus have a low resource potential. Hot springs of moderate discharge occur adjacent to the area and are utilized as hot baths. No hot springs are known in the study area and thus the potential for geothermal energy is low. INTRODUCTION roads from Greenfield and King City provide access from the east. A paved road from Jolon crosses the range and reaches Area description the coast just south of the area. The study area has rugged relief and dense vegetation. The Ventana Wilderness encompasses approximately Cone Peak, only 3.2 mi from the Pacific Ocean, has an eleva­ 159,000 acres, of which 98,000 acres was initially designated tion of 5,155 ft. Junipero Serra Peak, with an elevation of as a primitive area and 61,000 acres was later added. This 5,862 ft, is the highest peak in the Santa Lucia Range. Much report deals with the areas added to wilderness together with of the area is covered by brush, with stands of oak, madrone, the Black Butte, Bear Mountain, and Bear Canyon Roadless and pine in more moist locations and at higher elevations. Areas. In all, they comprise about 116,000 acres in the Los Redwoods occur in valleys near the coast. The large Marble Padres National Forest, Monterey County, Calif, (fig. 1). For Cone fire of 1977 burned much of the study area north of The the purpose of this report the areas will be referred to collec­ Indians ranch, temporarily eliminating a great deal of nearly tively as the study area. impenetrable brush. Annual precipitation ranges from more The study area is located in the Santa Lucia Range than 100 in. near the coast to about 20 in. inland, falling between U.S. Highway 101 and California Highway 1. Paved mainly between December and April (Pearson and others, 1967). rite, but diorite and gabbro bodies also occur. The largest intrusive bodies are near Junipero Serra and Pinyon Peaks Previous investigations (fig. 1). A few small ultramafic intrusions, some with unusual zoned structure, are spaced widely within the granitic and Numerous reports deal with the geology of the study high-grade metamorphic rocks. Charnockitic tonalite is area. Geologic maps with discussions of the mineral re­ found in the southwestern part of the area (Compton, 1960). sources of parts of the area have been published by Reiche Both the igneous and the metamorphic rocks contain abundant (1937), Fiedler (1944), and Durham (1963, 1970, 1974). Other dikes and pods of pegmatite. Radiometric dating suggests an geologic maps are published by Dibblee (1974), Dickinson emplacement age of 100-110 m.y. (middle Cretaceous) for the (1965), Wiebe (1970), Graham (1979), and Ruetz (1976). The granitic rocks of the northern Santa Lucia Range (Mattinson, area is included in maps of the northern Santa Lucia Range 1978; Ross, 1978). showing reconnaissance geology (Ross, 1976a) and the distri­ The igneous and metamorphic rocks are overlain bution of metamorphic rocks and minerals (Ross, 1976b). The unconformably by sedimentary rocks, mainly sandstone, economic geology of the area is included in Hart's (1966) mudstone, and conglomerate. These rocks show complex study of the mines and mineral resources of Monterey stratigraphic relations and have been assigned various strati- County. Limestone and dolomite resources are described by graphic names (Durham, 1974; Graham, 1979). South and Hart (1978). Gribi (1963) discusses the petroleum geology of west of The Indians the sedimentary rocks are mainly Late the region. The mineral resources of the original Ventana Cretaceous and Paleocene in age. North and east of The Wilderness adjoining the present study area have been inves­ Indians, Paleocene to Miocene age rocks are present. The tigated by Pearson and others (1967). Monterey Formation (Miocene) is a distinctive mudstone unit rich in foraminifers and containing porcelaneous and diato- Present investigation maceous beds. Many rock samples of the Monterey emit a fetid petroliferous odor when freshly broken. In the study The U.S. Geological Survey conducted geologic, geo- area the Monterey is the youngest sedimentary unit exposed. chemical, and geophysical investigations to evaluate the Sand and gravel occur in alluvium and alluvial terraces mineral resource potential of the area. Previous geologic along most streams. These bodies are generally small, but mapping was compiled and modified by additional observa­ near The Indians two broad tongues of bouldery alluvium tions to produce a geologic map of the study area at a scale extend 1 and 3 mi into the mountains along minor streams. of 1:50,000 (Seiders and others, 1983). Geochemical studies chiefly involved the collection and semiquantitative analysis Geochemistry of stream-sediment samples. The analytical results were examined statistically to reveal anomalous concentrations of Stream-sediment samples were collected at 167 local­ elements. An aeromagnetic survey was conducted by R. J. ities. An attempt was made to sample sedynent from each Blakely, (unpub. data, 1982). The U.S. Bureau of Mines re­ drainage basin with an area of about 1 mi and to collect viewed Monterey County records to determine claim loca­ samples along trunk streams at 2 mi intervals. The minus-80- tions. An attempt was made to locate and examine all claims mesh fraction of each sample was analyzed by semiquanti­ and prospects in the field. Chip and grab samples were taken tative spectrographic methods (Motooka and Grimes, 1976) from outcrops, dumps, and float, and placer samples were for 31 elements (Ag, As, Au, B, Ba, Be, Bi, Ca, Cd, Co, Cr, taken from streambeds and slopewash. Scintillometers were Cu, Fe, La, Mg, Mn, Mo, Nb, Ni, Pb, Sb, Sc, Sn, Sr, Ti, V, W, carried during fieldwork in an attempt to detect anomalous Y, Zn, Zr, and Th). Each sample was also analyzed by instru­ radioactivity. Lode and placer samples were also checked for mental methods for mercury (limit of determination, 0.02 radioactivity and fluorescence. ppm (parts per million). Eleven samples representing large drainage areas were analyzed by atomic-absorption spectro- GEOLOGY, GEOCHEMISTRY, AND GEOPHYSICS photometry for gold (limit of determination 0.05 ppm).