DEBRIS-COVERED MESAS OF BOULDER, COL. 



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has proportionately less 

 sandstone, more meta- 

 morphic, and more gran- 

 itic material, the latter 

 in a much decomposed 

 state ; and third, the re- 

 cent valley drift, com- 

 posed mainly of well 

 rounded crystalline ma- 

 terial of which unde- 

 composed granitic rock 

 forms a large part. 



There is one other 

 group of phenomena 

 which must be consid- 

 ered before attempting 

 an interpretation. There 

 is a large mesa near the 

 mouth of Bear Canyon 

 (see map, Fig. 1) on 

 which the largest bowl- 

 ders are found in great 

 numbers. This mesa is 

 also the highest in the 

 region under discussion. 

 A line drawn from its 

 top, parallel to the foot- 

 hills and touching the 

 tops of the mesas to the 

 north, would have a gen- 

 tle slope in that direc- 

 tion, i. e., toward Boul- 

 der Creek. A similar 

 though indistinct slope 

 toward South Boulder 

 Creek is indicated by 



