CHAPTER XVIII. 
GEOLOGY OF THE DISTRICT FROM SAM DIEGO TO FORT YUMA. 
TeRTIARIES OP SAN DIEGO.-VOLCANIC ROCKS NEAR SAN PASQUALE.—SAN YSABEL.- Axis OF THE CORDILLERAS.—WaRNEr’s 
RANCHO.- AgUA CALIENTE.-MINERALS IN THE GRANITES OF SAN FELIPE.-SPRINGS OF.-PoRPHYRITIC ROCKS BETWEEN 
SAN FELIPE AND VALLECITAS.-SPRINGS AT LATTER PLACE.-ThE CORDILLERAS —ThEIR BREADTH, ALTITUDE, AND STRUC¬ 
TURE.—Volcanic intrusions in.—Included gneiss.—Probable age of the range.—The Colorado desert.—Tertiaries 
AND ALLUVIUM.—CURVED BEDS. EXCESSIVE TEMPERATURE.—PHYSICAL APPEARANCE OF THE MARGIN.—SACKETT’s WELLS, 
SOIL AT WATER OF.—IGNEOUS ROCKS OF DESERT.—LAGOONS.—ALAMO MOCHO.—WELLS AT, AND SUPPLY OF WATER.—SLOPE 
OF THE DESERT.-ItS VEGETATION_ClIMATAL PHENOMENA.-TRAIL TO COOK’s WELL.-DRIFT SANDS.- On NEW RIVER, 
AND THE PRESENT FLUVIATILE ACTION OF THE COLORADO.-AlGODONES.-COLORADO RIVER-FORT YUMA.—Of THE CLIMATE 
AND WATER SUPPLY OF THE DESERT. 
The low hills which surround the mission of San Diego, and which form the headlands along 
the extremities of the harbor, are of the tertiary period, and are similar in character to those 
existing at Los Angeles and further north to the San Buenaventura river. 
These tertiaries stretch inland, forming a high terraced country, which continues to ranchos 
Solidad and Penascitas. Trappean and augitic dykes commence to show themselves east of 
this, and the character of the country changes, becoming more rugged and elevated, until San 
Pasquale is reached, where the underlying rock is a soft felspathic granite. The direction of 
the granitic ranges here is south 70° west, cut through by a finer grained porphyry granite 
running east and west; here and there the granite contains hornblende crystals, hut never for 
any distance, returning again to the micaceous variety ; further east, at “ Lagoons,” (11 miles,) 
it becomes coarser, with well defined crystals of orthose ; these hills enclose small valleys between 
them, well supplied with springs, some of which, coming from deep sources, are warmer than 
the atmosphere in winter time. 
San Ysahel mission is situated among the fertile valleys near the summit of the sierra. 
Granite constitutes the only rock visible; it is a coarse felspathic variety, and has masses of 
gneiss and mica slate imbedded in it. 
From San Ysahel the trail leads through a granitic canon, the hills on each side of which 
cannot he less than 2,000 feet high. Bear Warner’s rancho is a hot spring, “agua caliente,” 
which issues out of a cleft in the granite, and has a temperature of 135° Fahr. The granite 
between the rancho and San Felipe is soft and felspathic, with brownish mica in moderate sized 
plates, and, as at San Ysahel, is not homogeneous, hut contains masses of gneiss imbedded in 
it; here also occur veins of quartz with imperfect crystals of dark tourmaline, (schorl.) 
The valley in which Warner’s rancho is situated has a slight slope to the southeast. On the 
western side, at the base of the hills, are some marks of terrace action. 
At San Felipe, the river, which a few miles higher up was flowing, had disappeared, and its 
course was indicated by the growth of salt grass, rushes, and a saline efflorescence of common 
salt, gypsum, and carbonate of potass. The soil is composed of the debris of the felspathic 
granite. The massive rock here is syenite, composed of lamellar hornblende, and white felspar, 
with, here and there, occasional plates of mica, and some quartz. Through this a vein of 
