SANTA CLARA VALLEY : MODELO FORMATION. 
19 
SHALE IN THE MODELO. 
The two sandstones described above are divided by a body of earthy 
shale, gray to brown, which bears limestone concretions weathering 
yellow and whose thickness has been variously estimated at 400 to 
1,600 feet. Overlying the upper sandstone is a second body of shale, 
of uncertain thickness owing to the fact that in the region under dis¬ 
cussion not only has erosion removed the sediments down to an unde¬ 
termined horizon in the formation, but an unconformity also exists 
between this and the overlying formation. However, the thickness is 
variously estimated at between 200 and 1,500 feet, according to 
locality. This shale is indistinguishable from that separating the two 
Modelo sandstones already described. Both vary from a granular, 
siliceous type to one of an earthy and fissile character, more readily 
breaking down under the influence of weathering. The color of the 
lower bed is commonly light gray; that of the upper may be brown, 
gray, or yellowish. Both bodies carry calcareous layers and here and 
there lenticular limestone concretions that weather yellow. Were 
the upper sandstone to disappear the shales above and below would 
become a single mass, uniform in their general features, from top to 
bottom; were both sandstones to disappear it would be difficult to dis¬ 
tinguish these rocks from the upper portion of the Vaqueros formation. 
They would be more readily differentiated from the lower portion of 
the Vaqueros, however, by the variety of color in the older beds and 
by the marked change to the rusty, calcereo-arenaceous grit at their 
base. 
VARIATION IN COMPOSITION OF THE MODELO. 
The foregoing paragraphs describe what appears to be the normal 
section of the Modelo formation, but the aspect varies somewhat from 
point to point, by reason of the subdivision of the sandstones and the 
changes in their relative porportion to the formation as a whole. At 
the head of Modelo Canyon, for instance, the outcropping portion of 
the lower sandstone appears to be split into two bodies, each 300 feet 
thick, by 60 to 100 feet of shale, and a similar division is shown by 
the logs of wells drilled in this canyon. What may prove to be the 
upper sandstone is separated from the lower by only about 200 feet 
of brown shale as compared with 400 to 1,600 feet in the normal sec¬ 
tion. The enormous development of the Modelo sandstones in the 
lofty divide separating Tar Creek from the drainage of Hopper Canyon 
and Piru Creek is also at variance with the average thickness of either 
of these members, and it may be that the shales are reduced to a 
minimum in this locality, resulting in a sandstone facies for this 
formation amounting to at least 2,000 feet. 
South of Santa Clara River the Modelo formation is unrecognized, 
nor is it possible to find for it a proved correlative. Certain sand¬ 
stones assigned here to the Vaqueros terrane carry concretions that 
