GEOLOGIC RECONNAISSANCE IN BAJA CALIFORNIA — 745 
of a sheet which flowed down the canyon when it had only about 
half its present depth. It is possible, however, that this lava sheet 
is included in the mesa sandstone, for such a relation is shown 
on the south side of the canyon 12 miles below Comondu, just 
above the mouth of the Arroyo Belamote. In that vicinity also 
there are some conglomerate members showing strong unconformity 
at base, and a few conglomeratic layers are included in the gray 
sandstone. It is probable that the mesa-sandstone outcrop extends 
down the Arroyo Comondu to Rancho San Andreta, near the mouth 
of the arroyo, where the following section is exposed: 
onplomerdteni sais cars ceases welermeonare tera 30 feet, many fossils 
Grayssand, paleyereenish’ tints. ac. -s cece 20 feet 
imypledre yellowish. Majer omits 5 feet exposed 
Fossils collected from the basal bed in this exposure were 
determined by Dr. Gardner as Turritella, Cytherea and Balanus ?, 
and a Chione resembling C. elsmerensis English, probably Pliocene 
in age. This is the only paleontologic evidence that I obtained 
as to the age of the formation and it is not conclusive. 
Extensive exposures of mesa sandstone are presented in the 
Arroyo San Benancio and the Arroyo San Andres south of Com- 
ondu, one of which is shown in Figure 22. The sandstone, con- 
glomerate, agglomerate, tuff, etc., constitute cliffs and high canyon 
walls along the west side of the Gulf of California from Agua 
Verde Bay to Canyon de los Reyes. A section in the latter shows 
the following features: 
GENERALIZED SECTION OF STRATA IN CANYON DE LOS IES 
Feet 
Soft, gray sandstones, some beds conglomeratic (top 
(OVE TaKGhod®) uate Ar a MEN I RR aetna oR Ee ene 220 
Rhy olite tows (bench-maker)) ae catei-ete rae ake 40 
Soft, gray sandstone, several beds of conglomerate 
TOMEMOVEASESiscic ersten Amie a atonslecdohetateeneuee oretons 260 
Conglomerate with pawliees of igneous and other 
crystalline nOCKSH wr miarqamiee sr eetsyeretensereaniok 40 
Rhyolite flow (making wide bench)............. 30-70 
Gray conglomeratic sandstone with agglomerate 
Ney Chasers at hooey PRE REP RSEIS OGIO ort casos 200 
Agglomerate, tuff, volcanic ash, igneous sheets. 
Bedding massive extends to tide-level......... 650 
Motalithickmesswe sd) Getic cise see cls cters 1,650 
