364 CARNEGIE INSTITUTION OF WASHINGTON. 



2. Surface Displacements. 



The plan of spreading an accurate network of primary triangulation over 

 those regions of California which are particularly subject to earth-movements 

 has made splendid progress during the past year. The U. S. Coast and Geo- 

 detic Survey obtained an appropriation of $15,000 for beginning this work in 

 Jul}^ 1922, and during that year measured a double system of triangles from 

 the Sierras (Mount Lola and Round Top), across the Great Valley 

 and the Coast Range, to the Pacific Coast. During the past year, under 

 a continuance of the appropriation, the triangulation has been continued 

 southward along the coast and is expected to reach nearly or quite to the 

 Mexican boundary before the close of the present season. 



The Coast and Geodetic Survey has been much interested in this work and 

 has put forth an extraordinary effort to carry it out with the highest precision 

 attainable. Although the results of these surveys have not yet been reduced 

 and formulated, it is possible to say that a great many displacements have 

 occurred since the last survey, including one which is of particular importance 

 and affects all of the measurements which were made in connection with the 

 great San Francisco earthquake of 1906. It will be recalled that in the two 

 field seasons following the earthquake (1906-1907) a careful survey of the 

 disturbed region was made under the direction of Mr. Hayford, which sub- 

 sequently formed the basis of a report by the Coast and Geodetic Survey 

 (Hayford) and one by the Carnegie Institution of Washington (A. C. Lawson). 

 Upon these reports our present information regarding that great disturbance 

 mainly depends. Hayford's triangulation of 1907 was referred to the Mocho- 

 Diablo base-line, but no survey connecting this base-line with the crest of the 

 Sierras was made at that time. Now that the present survey has revealed the 

 fact that this base-line has shifted its position since the last survey some 30 

 years ago, we are left at a loss to know what its position may have been 

 at the time when the earthquake survey was referred to it in 1907. 



This situation may serve to emphasize, if emphasis be needed, the vital 

 importance of these surveys at appropriate intervals as a preliminary to any 

 serious discussion of earth-movements in California. 



Similarly, the work of the past summer, although still incomplete and in 

 no sense ready for discussion, has, nevertheless, clearly shown many such 

 displacements, some of 20 feet or more, along the coast between San Fran- 

 cisco and the Mexican boundary, of which we had no intimation from any 

 other source. The further study of these data should also tell us plainly 

 whether we are dealing here with a number of independent displacements 

 revealing zones of structural weakness and local movement or whether we 

 have to recognize a general crustal creep of this region. The value of this 

 information, whether considered from the economic or the scientific view- 

 point, is immediately obvious. 



3. Southern California. 

 In the report of last year attention was called to the fact that our geological 

 knowledge of the southern part of the State was less complete than of the 

 northern part, except possibly in a few regions which have been especially 

 examined for oil deposits. Accordingly the major portion of the time of 

 Mr. H. 0. Wood, Research Associate in Seismology, and of Messrs. L. S. 

 Noble and W. S. W. Kew, of the U. S. Geological Survey, has been devoted to 



