54 
STRUCTURE OF THE CUYAMA VALLEY. 
stream, or wholly disappear, were it not compelled to enter the Santa Lncia range, and thus 
receive from its well watered summits numerous additional rivulets which swell up its lower 
channel as it enters Guadalupe Largo plain. 
The valley is hounded on the east by the prolongation of the San Jose mountains—these, 
which have been already described as the continuation of the Point Pinos range, extend up the 
valley in a southeasterly direction ; in its course it sends a spur in a more southerly line into the 
valley—while the main chain further east continues to form the boundary between it and Estero 
plain to within 20 miles of the termination of Tulare valley ; in so doing, it appears to lose the 
character of mountains, and to resemble low hills hounding the plain ; but the fact is, that the 
valley of the river rises considerably in level, the elevating force being spread over the area of 
the Santa Maria valley in its upper course. The hills in the southern extremity, where it 
separates the valley from Estero plain, are mostly porphyritic felspar, containing albite in well 
marked hexagons. The hills are rounded swells, which have deep valleys or breaks between 
them, allowing of passes from Tulare valley and Estero plain into the valley of this river. 
These porphyry domes present the appearance of a series of wash-basins inverted. Estero plain 
is properly a longitudinal valley in this range, being uplifted by it to an elevation considerably 
exceeding that of the valleys on either side ; for while both Tulare and Santa Maria valleys roll 
their waters north, Estero plain sends its stream, the Agua de Paleta, in a southerly course into 
Tulare valley, the level of which is below that of the Santa Maria. 
This granitoid felspar porphyry range has a strike S. 40° E., with an exposed width of 7 to 
10 miles of elevated rolling hills, forming a true anticlinal axis, throwing the strata into Tulare 
valley with a dip of 15° to 20° eastward, and into Santa Maria valley on the west at an angle 
scarcely exceeding 15° to the N. W. The porphyritic rock may be traced south into the eastern 
and northern portions of the San Emilio mountain. 
The strata dipping toward the valley consist of 3 beds, as observed from above downward. 
1st. A hard, whitish, compact clay rock, absorbent to tongue, with veins of crystallized 
gypsum and cavities, where the crystals had weathered out; layers of silicified rock, occur 
through this bed; 120 feet of this stratum was observed. 
2d. Stratum of brownish yellow clay rock; gypsiferous, gypsum disseminated in amorphous 
masses, accompanied with seams of crystalline mineral; about 30 feet of this rock was exposed. 
3d. White quartz grit; pebbles rounded—a clay paste with seams of sulphate intercalated ; 
25 feet of this rock exposed. 
In the hasty survey made no fossils were observed, and the exact age cannot, therefore, he 
determined; in lithological character they resemble the lower gypsiferous sandstones of Panza 
hills and the beds of sandstone which lie above the conglomerate of Santa Margarita and 
Santa Inez. 
The gypsum is washed out readily from these strata into the plain, where, in low situations, 
it forms an efflorescent crust on the soil, and attaches itself as a thin frosting round the roots 
and stems of the grasses. 
At the northern and lower end of the valley the San Jose mountains form the eastern limit. 
The character of this range has been described under its appropriate head, and need only be 
slightly noticed here. The newest strata of that range dip into the valley at an angle of 25° 
to the southwest. The uppermost bed is the soft clay rock, containing impressions of area 
obispoensis, similar to that described in the San Luis valley as forming the most recent series in 
California. Upon these were found the terraces which stretched for many miles up the valley. 
