BAJA CALIFORNIA AND SONORA SYSTEMS 



481 



LAI 31° N 



Pacific Ocean 



Detritus of Colorado Riv 

 sierra san La Providencia & possibly older sed. 



pedro martir / valley of San Felipe ~~? S a. Enterada 



KmGrm ^^ \ .V^S IXOa/_ Qal Rulf of California! Ts Altar Desert > 



Probably faults in gulf bottom 



LAT. Z9° N. 



Cedros Is. 



Pacific Ocean *> Bay of Sebastian Viscaino 



Tt 



_ Ballenas / /7 ^ e/ ^ ,Q G "° rd ° 



lb Channel Tc Gulf of California 



7i^> 





Grm 



LAT. 2 7° N. 



Pacific Ocean 



Tb Qal To 



I /ono cfe. /as l//rgene5 /■ Tortuga 



Tt Ty Tb Tc 6u if f $ California 



Fig. 30.2. Cross sections of Baja California, after Beal, 1948. Positions designated by latitudes 

 are approximate. 



Grm, crystalline rocks of Nevadan orogeny, diorite varieties, schists, gneisses; Tb, Cenozoic 

 flows and intrusions, mostly andesite and basalt; Km, San Fernando formation of Cretaceous 



metamorphics, limestone, shale, quartzite and intrusive rocks; K, Rosario Upper Cretaceous marine 

 sandstone and dark shales; Tt, Tepetate silts, sandstones, Paleocene to Eocene; Ty, Ysidro sand- 

 stone, siltstone and tuffs, Miocene; Tc, Comondu volcanics and elastics, upper Miocene; Ts, 

 Salada formation, Pliocene. 



cross sections of Figs. 30.2 to 30.4. Inland southeastward from the Bay 

 of Sebastian Vizcaino is a vast desert of Quaternary alluvium about 800 

 feet above sea level. 



The Tertiary rocks are in two narrow belts along each side of the 

 Nevadan core in the northern part. Just south of latitude 30°, however, 

 the Pacific belt of Tertiary deposition (perhaps only the conglomerates 



and volcanics of the upper Miocene) extends across to the east coast. 

 Then from latitude 29° southward to the southern end of the peninsula, 

 the Nevadan rocks crop out in the bordering islands on both sides, in- 

 cluding the western cape region (Sierra Vizcaino). Finally, a large part 

 of the south end of the peninsula (Sierra Victoria) is made up of the 

 Nevadan complex. See the tectonic map, Fig. 30.1. 



