Earth and Planetary Sciences ETDs

Publication Date



The settlement of San Lorenzo is approximately 19 miles east of Silver City, New Mexico. The area consists of rolling hills, relatively steep slopes and the broad Mimbres River Valley. The land surface reflects partial erosion of Basin and Range fault blocks. The maximtun elevation is 7,170 feet, with relief of 1,400 feet.

The main structural feature is a northwest trending mountain range, which is a west-southwest-dipping fault block bounded on the northeast by the Mimbres fault. Vertical displacement ranges from 150 meters (500 feet) to 1,200 meters (4,000 feet). Rocks exposed along the steep northeastern escarpment range in age from Precambrian to early Paleozoic. Lesser faults of easterly trend dissect the Mimbres fault and are con­centrated in the western half of the mapped area.

Every geologic period, except the Triassic and Jurassic, is repre­sented by at least one fonnation. Above Precambrian diabase lie the following Paleozoic and Cretaceous limestone, sandstone and shale units: Bliss Formation (Cambrian and Ordovician), 44-55 meters (145-180 feet); El Paso Limestone (Lower Ordovician), 152-163 meters (500-535 feet); Montoya Dolomite (Middle to Upper Ordovician), 88-99 meters (290-325 feet); Fusselman Dolomite (Silurian), 27-53 meters (90-175 feet); Percha Shale (Upper Devonian), 69-99 meters (225-325 feet); Lake Valley Limestone (Mississippian), 91-117 meters (300-325 feet); Oswaldo Fonnation (Pennsyl- vanian), 99-122 meters (325-400 feet); Syrene Formation, (Pennsylvanian), 53-114 meters (175-375 feet); Abo Fonnation (Permian ), 67 meters (220 feet); Beartooth Quartzite (Upper(?) Cretaceous), 12-37 meters (40-120 feet). The Tertiary system is represented by volcanic and continental sedimentary rock which covers approximately one third of the mapped area. The volcanic and sedimentary section consists of: Rubio Peak Formation, 213 meters (700 feet); Kneeling Nun Quartz Latite, 244 meters (800 feet); Caballo Blanco Rhyolite Tuff, 69 meters (225 feet); Razor-back Fonnation, 229 meters (750 feet); Sandstone, conglomerate and tuff, 91 meters (300 feet); Bear Springs Basaltic Andesite, 229 meters (750 feet); Gila Conglomerate, 308 meters (1,010 feet); Terrace gravels, 31 meters (100 feet).

Silicification, epidotization, sericitization and secondary quartz and calcite fracture fillings are evident on a minor scale throughout the San Lorenzo area. Aside from propylitization there is nothing to indicate the presence of mineral deposits of economic value at this time.

Degree Name

Earth and Planetary Sciences

Level of Degree


Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Wolfgang Eugene Elston

Second Committee Member

Albert Masakiyo Kudo

Third Committee Member

J. Paul Fitzsimmons



Document Type


Included in

Geology Commons