GEOLOGIC RECONNAISSANCE IN BAJA CALIFORNIA 731 
Rancho Tepetate and for. some distance above and below that 
place (Fig. 8). Dips are all to the north or north-northeast at 
low angles. The outcrop of the formation extends up the Arroyo 
San Hilario to within about 4 miles of Rancho San Hilario where 
the top member is massive, pale buff sandstone with irony layers 
and many fragments of oyster shells. It dips north and apparently 
passes beneath the Monterey beds. There sandstones have yielded 
few fossils, but echinoid spines and foraminifera are abundant at 
Rancho Tepetate, and oysters and a shark’s tooth near Rancho 
Santa Teresa all appear to indicate Eocene age. Evidently the 
exposures are due to a mound of the formation extending southeast 
and southwest with altitude sufficiently great in the region from the 
Arroyo Salado to the Arroyo Conejo for the strata to be revealed 
by erosion in the deeper valleys. 
MIOCENE 
Monterey beds.—In the vicinity of the oases of La Purisima and 
San Hilario I found small exposures of strata so closely resembling 
the Monterey formation of southern California that tentative 
correlation seems desirable. Outcrops extend along the Arroyo 
de la Purisima from 2 miles above tidewater to within 6 miles of 
La Purisima and a small one appears in the upper part of the latter 
village. Outcrops also extend along the valley of the Arroyo San 
Gregorio for a mile or more about to miles southwest of La Purisima, 
and smaller crops appear above Purisima Vieja and San José, 
respectively 15 and 20 miles northwest of La Purisima, and on 
the Arroyo San Raimondi, 35 miles northwest of La Purisima. 
The same beds appear in an area of 2 or 3 square miles a short 
distance west of San Hilario, and in small crops of steeply upturned 
beds appearing at intervals from a point a mile northwest of San 
Luis to a point 15 miles southeast of that place. The relations are 
shown in sections 13, 14, 17, 18, and 19, Figures 3 and 4. At most 
places the beds are more or less tilted and flexed, and various 
younger formations overlie them unconformably, as shown in Fig- 
ures 9 and 10, although at several places where the strata are not 
flexed there appears to be gradation into the overlying “yellow 
beds.” 
