70 GUIDEBOOK OF THE WESTERN UNITED STATES 
Edwards Plateau, and at the head of a deep canyon about 25 miles 
west-northwest of San Antonio it is dammed to make 
Lake Medina, a large storage reservoir and an attrac- 
Sabie sae alge tive resort. The dam is 164 feet high and 1,580 feet 
New Orleans 597 miles. long. The water diverted into a canal some distance 
below the dam is carried along the ridge west of Cas- 
troville to be used for irrigation in the region south. This canal is 
crossed by the railroad at Pearson siding, 4 miles west of Lacoste. 
The Medina River along the railroad carries but little water because 
of the dam 15 miles above that diverts most of the flow into the irriga- 
tion canal. In an exposure of the Escondido formation in a cut 
about 5 miles west of Macdona there is yellow limestone at the top, 
2 feet, with a thin fossiliferous layer; yellow shale, 5 feet; yellow im- 
pure sandstone, 4 inches; and yellow-brown shale, 3 feet to the base. 
The beds dip about 1° SW. The railroad is deflected to the south to 
carry it around the south end of a high ridge of Escondido shale 
which extends along the west side of the Medina River Valley in the 
Castroville region,® north of the railroad. The higher part of this 
ridge is capped by gravel of a high-level terrace, the Uvalde Plain, 
of which there are many remnants in the region west of San Antonio. 
From Pearson siding northwestward for 10 miles the railroad is 
mostly in a valley in clays with limy layers, of the basal group (Mid- 
way) of Tertiary age. The continuity of the strata is broken by 
several faults, mostly trending east-northeast, which bring up the 
underlying Escondido formation obscurely exposed at intervals. 
Just beyond Dunlay the railroad crosses a low ridge consisting of 
shales with hard sandstone layers of the Escondido formation. On 
both sides of the pass through which the railroad goes 
Dunlay. are plateau remnants of moderate height in which the 
ioe Escondido beds are overlain by the Midway group, 
New Orleans 611 miles. Which is capped by old terrace gravel deposited when 
the drainage system of the region was about 200 feet 
less deep than it is at present, a feature referred to on previous pages. 
Lacoste. 
Elevation 718 feet. 
® Castroville was founded by and 
‘named for Count Henri de Castro, who 
in 1844 brought there a colony of French 
and Alsatians. The architecture is 
largely of French rural type, with slop- 
ing roofs, small windo 
blinds. 
83 In the region between San 
and Del Rio, baer aeson 
Upper Cretaceous formations continue 
most notable features is the devel- 
opment of the Anacacho limestone, 300 
feet or more thick, replacing the Taylor 
shale, and merging westward into the 
Upson clay and the San Miguel forma- 
tion. The Navarro shale also merges 
laterally to the west into the Escondido 
formation, which may be 700 feet thick 
in the Uvalde region. 
are represented diagrammatically in 
Figure 6, which, however, necessarily 
has a greatly exaggerated vertical scale. 
The Midway, the lowest formation of 
the Tertiary system in this region, lies 
SPSUDIGBARNY. on the Escondido for- 
mation ( extension of the Na- 
varro shale) with but little discordance 
of dip. 
