In 1852 a survey was made of the southwestern edge of the Mojave Desert. The Old Spanish Trail # had become a wagon road bringing thousands of pioneers to the west and developed as a supply route between Los Angeles and Salt Lake City. The survey was as accurate as any at that time and followed the trail from near the top of the Cajon Pass to a point where the trail leaves the Mojave River near Fishponds. The trail to Salt Lake continues north as we know it, but the river flowing east on this map bears southeast and empties into the Colorado River. At the time it was thought the Mojave (spelled Mohahve on the map) River followed this course. It did not. There was no Mojave Road in 1852 and not many Americans had traversed that portion of the desert. As we now know the Mojave River cuts through Afton Canyon and then disappears into the sink of the Mojave before it reaches Soda Lake.
Playa formation – “A playa is a dry, vegetation-free, flat area at the lowest part of an undrained desert basin. It is a location where ephemeral lakes form during wet periods, and is underlain by stratified clay, silt, and sand, and commonly, soluble salts. Playas occur in intermountain basins throughout the arid southwestern United States. Although playas may appear as featureless plains, they are rich in features and characteristics that can reveal information about climates, past and present. “
Rand Schist of Rand Mountains, Schistose rocks of Rand Mountains described briefly ·by Hess (1910, p.28-29, 46) and by Hershey (1902a, p. 273); named, described, and mapped as Rand Schist by Hulin ( 1925,p. 23-31, pl. 1), and officially adopted for use in this report.
Rand Schist folded into anticlinal arch plunging gently westward as indicated by foliation attitudes (figs. 3, 4). On north, schist overlain by gneissic rocks (Johannesburg Gneiss of Hulin), separated by possible fault or thin zone of cataclastic(?) transitional rock; on south and near Randsburg, schist intruded by quartz monzonite; extends unknown distance westward under ·alluviated valley, possibly to Garlock fault. Possibly 10,000 feet of schist exposed; lithology identical to that of Pelona Schist of Sierra Pelona and of Tehachapi Mountains; gray schist, predominating over green schist, contains occasional pods of fibrous actinolite schist; thin layers of quartzite and of marble, mostly in southern and western exposures. In exposures northeast of Johannesburg, albite content of schist increases to 75 percent.
Type locality of Rand Schist designated as generally north-dipping section in Rand Mountains (fig. 4), from quartz monzonite intrusion just south of Randsburg northward to contact with overlying(~) gneiss about 3 miles north of Randsburg.
Areal Geology of the Western Mojave Desert California By THOMAS W. DIBBLEE, ]R. GEOLOGICAL SURVEY PROFESSIONAL PAPER 522 – 1967