44 University of California Publications in Geology [Vol. 8 



valley, where deposition took place close to shore and in shallow water, 

 the beds are composed of soft unindurated sandstone, but toward 

 Coyote Mountain near the mouth of the valley they become finer- 

 grained and contain more shale. Under erosion the rocks of the Upper 

 Division yield forms characteristic of badland topography. The 

 monotony of this is occasionally broken by a harder stratum of a 

 more indurated sandstone or of a hard gray shale which forms a ridge 

 or a residual capping. The upper series contains no eehinoderms and 

 only a meagre fauna. There are a few strata which are composed 

 almost entirely of Ostrea vespertina and Anomia subcostata. The 

 Upper Division extends north along the west side of the Salton Sea 

 to the Santa Rosa Mountains, which is the most northerly limit of the 

 beds in this region. Just north of the Superstition Mountains, which 

 are residuals of coarse granite rising above the valley floor, these soft 

 sandstones and shales were found to contain numerous shells of 

 Rangia, sp., which would indicate that in the northern extremity of 

 the Gulf of California, at the time of deposition of the beds, the water 

 was brackish. 



Coyote Mountain Locality. — The mass of Coyote Mountain consists 

 mainly of hard granitic and metamorphic rocks. It rises abruptly 

 from the flat floor of the desert, giving rise to sharply-sloping talus- 

 covered slopes cut by steep-walled gorges. The streams on reaching 

 the lower levels have cut box-like channels to a depth of at least 

 seventy-five feet into the andesite, which lies directly upon the older 

 rocks on the southeast side of the mountain. In the softer Tertiary 

 sandstone, especially on the Carrizo Creek side, the streams widen, 

 and a badland topography is produced. The drainage lines end in 

 meandering washes upon the desert. 



The core of the mountain is a structurally complex series consisting 

 mainly of coarse marble, garnitiferous schist, quartzites and granites. 

 Coarse pegmatite dykes containing tourmaline, feldspar, quartz, and 

 muscovite are also found cutting these rocks. Into all has been in- 

 truded dykes of a black aphanitic rock. These formations are the 

 oldest in the region and have been assigned to the Carboniferous by 

 Fairbanks 8 on scanty palaeontologic evidence. 



Resting upon the basal complex is an andesitic lava with associated 

 mud flows, the lava and mud flows aggregating from two to three 

 hundred feet in thickness. Interstratified with the lava and mud 



s Fairbanks, H. W., Eleventh Annual Eeport of the State Mineralogist of 

 California, p. 90, 1893. 



