J. L. Rich — Large Bowlders in Gravel Deposits. M3 



great waste-filled basins which make up a considerable part of 

 southern New Mexico, but separated on the north from its 

 parent high lands by a gravel-free lowland, 3 to 5 miles in 

 width, developed to old age on shales and intrusives of 

 moderate resistance. From the highlands on the east it is 

 separated by a relatively narrow valley. The gravel plain 

 faces the lowland to the north as a low, irregular escarpment 

 50 to 100 feet in height. 



On the northwestern border of the lowland, near Pinos 

 Altos, stands a group of conical peaks of intrusive rocks. 



Fig. 3. 





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•_,.,', *;3h v / . ; / -LJ*'\ 4 ii'V^ 



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Fig. 3. One of the large bowlders in the group at X (fig. 1). Note size 

 in comparison with the horse. In middle ground is the gravel-free inner 

 lowland between the gravel plain and the mountains which appear in the 

 background. 



Bounding it on the north and northeast, and running in a 

 direction a little south of east, is a great, sub-maturely dissected 

 escarpment of flat-lying lavas — rhyolites at the base and basalts 

 above — rising 1500 to 2500 feet above the general level of the 

 lowland. On the east of both lowland and piedmont gravel 

 plain stands a similar escarpment of lesser height, capped 

 mainly by rhyolite, overlying thick and relatively weak gravels 

 and tuffs. A temporary stream at the base of this escarpment 

 keeps it sharp in outline, and continually retreating. 



