THE 
AMERICAN GEOLOGIST. 
Vol. XXXIV. SEPTEMBER, 1904. No. 3. 
THE ORBICULAR GABBRO OF DEHESA, 
CALIFORNIA.* 
B3' H. H. Kesslkr and W. R. Hamilton, 
Stanford UniTersity, Cal. 
PLATES VI— X. 
Occurrence. The rock which forms the subject of this pa- 
per was first found in 1901, as a small piece of float, beside the 
road, near Dehesa, by Mr. ]\Iarion Powers. This specimen 
was sent to professor A. C. Lawson at the Universit}- of Cali- 
fornia and was discussed hy him in a brief paper before the 
Cordilleran Section of the Geological Society of America, at 
its meeting of December, iQOi.t Since the work of prepara- 
tion of the present paper has been completed, there has come 
from the press, a paper by professor Lawson on the saine sub- 
ject.! 
The orbicular gabbro occurs in a boss of gabbro which 
broke through the surrounding granite and which forms nearly 
the whole of the first hill which rises to the northwest of De- 
hesa post office. This hill is very steep and rises to an ele- 
vation of 1800 feet above sea level and 1300 feet above the 
Sweetwater river, which flows at the base. 
The locality is on the El Cajcn sheet of the V . S. Gcol. 
Survey, the exact locality being Long. 116° 52' \\'.. Lat. N. 
32° 47'. This gabbro boss has an area of approximately one 
• The authors are indebted to Dr. J. P. Smith, of Stanford University, for 
advice and assistance. 
t On an Orhiciilar Gabbro from San DicRO Co., Cal., by Anhrew C. Law- 
son, Berkeley, Calif. Science, (New Series), vol. xv, p. 415." 
t The Orbicular Gabbro at Dehesa, San Diego Co.. Cal.. bv .\NnRRW C. 
Lawson. Bull. Dept. Oenl. Vnir. Cal., vol. iii. No. 17, March. 1904 (The 
writers had begun preparation of this paper before they knew that the pai)er 
of Prof. Lawson was being prepared.) 
