BULLS HEAD DAM SITE.

In an investigation for the Bulls Head dam the first proposed site was abandoned. Back of the rocky river hills there was exposed a contact point of clay and sand at sufficiently low elevation to jeopardize a 100-foot dam at this place. Such a structure here would create a

CROSS SECTION LINE 3, DAM SITE NO. 2

CROSS SECTION DAM SITE NO.-2

FIG. 10.-Cross section, Bulls Head dam site No. 2, Colorado River.

reservoir with a capacity of 845,000 acre-feet and a surface area of 16,750 acres. While the conditions are unfavorable for so high a dam, a dam 60 or 70 feet above low water may possibly be constructed, provided bed rock is suitably close to the surface. A dam 70 feet in height would form a reservoir of 392,000 acre-feet capacity, with a

surface area of 13,600 acres. In consideration of this fact, it is deemed advisable to continue the investigations here in the future. The capacity and surface acreage are computed only to the northern limit of the area mapped (lat. 35° 36'). Where the canyon begins it is not believed that the portion of the reservoir in the canyon will increase the capacity to a large extent.

FIG. 11.-Cross section, Bulls Head dam site No. 2, Colorado River.

At the lower end of Pyramid Canyon, where the walls of the canyon and the neighboring hills presented good surface conditions for a high dam, an extended series of borings was made for bed rock, but with unsatisfactory results.

DIVERSION AT BULLS HEAD FOR NEEDLES VALLEY.

Though no suitable place for a high dam has yet been found at Bulls Head, it is feasible to construct here a diverting weir about 20 feet in height above low water, with wasteweir founded on solid rock on the Arizona shore. From this weir could be carried a canal which would cover 47,000 acres of land in Arizona between Bulls Head and Mellon.

FIG. 12.-Plan of borings, Bulls Head dam site No. 2, Colorado River.

Opposite Fort Mohave the river has changed its course from the bluffs on the Nevada shore to the bluffs on the Arizona shore. It appears probable that the river could be restored to its former course at a small expense, so that 10,600 acres which are now on the west side of the river would be on the east side and under the ditch, making a total area of 57,600 acres under the proposed canal. Of the area, 36,000 acres were classified as first- and second-class farming land.

The capacity of the Bulls Head reservoir at different heights of dam and the classification of the irrigable lands of Needles Valley below the reservoir are given in table on page 136.

About 6 miles below Bulls Head, at Hardyville, the river has a "hardpan" bottom, and it might be possible to divert it here by a low weir, but the project has not been investigated.