GEOLOGIC RECONNAISSANCE IN BAJA CALIFORNIA 733 
Yellow beds.—Under this title I shall group deposits of late 
Miocene age exposed extensively along the western slope of the 
peninsula trom latitude 29° to latitude 24°. They are mostly 
soft, loamy sandstone and sandy clay of pale straw-yellow tint 
with local limy beds, the latter generally full of fossils. Some 
contemporaneous igneous rocks are included in places. The 
yellow beds have an ag- 
gregate thickness of 500 
feet near the coast be- 
tween San Ignacio and 
La Purisima, although 
at the latter place the 
amount is not more 
than 120 feet. Asstated 
above, there is uncon- 
formity between this 
formation and the Mon- 
terey beds, only notice- 
able, however, where the 
latter Pare flexed; the 
overlying “‘mesa_ sand- 
stone” is also uncon- 
formable, as shown in 
Figures 11 and 12. 
The yellow beds are 
first noticeable in thin, 
scattered bodies lying on Fic. 10.—Steeply tilted Monterey beds on east 
the metamorphic menice side of the Arroyo de la Purisima, six miles below . 
La Purisima, Baja California. 
near latitude 29°. Near 
Jatitude 28° 30’ they have the relations shown in section 7, Figure 2, 
having been preserved from erosion by a thick cap of basalt. This 
relation continues for many miles south, as shown in sections 8-15, 
although the floor of metamorphic rocks sinks out of sight a short 
distance south of Calmalli. In the La Purisima region and near 
San Hilario the underlying formation is the rather uneven surface 
of the Monterey beds. Probably the formation thickens consider- 
ably under the Santa Clara Desert, where doubtless it is underlain 
