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WALTER C. MENDENHALL 



with a diminishing proportion of volcanic pebbles. Above them are 

 quartz conglomerates, tawny sandstones, and finally soft greenish- 

 yellow clay shales. 



An unconformity which is not especially conspicuous exists in the 

 Miocene between the sandy shell-bearing beds, loo feet or less in 

 thickness, which immediately overlie the volcanics or the metamor- 

 phics, and the great mass of shales, greenish or yellowish at base, 

 pink or pale red in general color-tone toward the top, which form the 

 bad-land area (Fig. 2) that is especially well developed between 



Fig. 2. — Lower Garnet Canyon and the adjacent bad lands cut in Miocene shales. 



Black and Carrizo mountains. Finally, across the planed edges of 

 these shale beds, a sheet of river cobbles, well rounded, has been dis- 

 tributed unconformably throughout the Carrizo Valley. They are prob- 

 ably Pleistocene, but are earlier than the silts, sands, and gravels, 

 which represent the offshore and beach deposits of the lake which 

 until recently has occupied the Colorado Desert. The latest erosion 

 has left these old stream deposits stranded upon the remnants of the 

 earlier valley floor at heights of from 100 to 200 feet above the present 

 bed of Carrizo Creek. 



DESCRIPTIVE 



Basal series. — The core of Carrizo Mountain (Fig. 9) is a series of 

 metamorphic rocks in which a blue or gray crystalline limestone is 



