1922] Hudson: Geology of the Cuyamaca Region of California 177 



INTRODUCTION 



This report on the geology of the Cuyamaca region is the result 

 of three months' field work carried on in the summers of 1917, 1918, 

 and 1919. During the first season the Friday Mine and the immedi- 

 ately adjacent country were the particular objects of study. In the 

 following seasons the general geologic investigation of the area was 

 carried on. 



A complete report on the geology of the region would contain a 

 chapter on the gold quartz veins. But time was not available for 

 more than a cursory examination of the mines of the Julian and 

 Banner districts, and nothing was learned that would add to the 

 knowledge already available in the literature. 1 



In the study of the geology of the Friday Mine particular atten- 

 tion was given to the ultimate origin of the deposit. For this reason 

 the secondary minerals of the ore receive only brief notice here. Sec- 

 ondary sulphides are present in small amount, but their development 

 has probably added little or nothing to the valuable metal content 

 of the ore. Time was not available for a complete investigation along 

 this line. 



The writer was assisted in the field by Mr. W. E. Inman in 1917 

 and is indebted to him not only for this work but for access to the 

 results of his study of the Friday Mine ores. Thanks are due to Mr. 

 G. H. Alvey for assistance in geologic mapping in 1918. To Messrs. 

 W. E. Sterne and Beecher Sterne, the principal owners of the Friday 

 Mine, the writer is grateful for the privilege of examining the prop- 

 erty. Without the assistance of Mr. C. M. Sterne the detailed invest- 

 igation of the mine would have been impossible. The writer is especi- 

 ally indebted to Professor G. D. Louderback, at whose suggestion this 

 work was begun and to whose encouragement and helpful criticism 

 the completion of the report is largely due, and to Professor A. C. 

 Lawson, who has pointed out fruitful lines of investigation. 



i See the various annual reports of the State Mineralogist, particularly the 

 reports for 1888, 1889, 1890, 1892, and 1914. 



