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CALIFORNIA

Lost Gold Ledge of the Chocolate Mountains

GEOLOGY OF THE AREA

The Chocolate Mountains are an elongated northwest-southeast trending range of uplifted, block-faulted Precambrian to Pre-Cretaceous igneous and metamorphic rocks intruded by younger Mesozoic granite plutons and younger still Tertiary volcanics. The range extends some 80 miles from the Laguna Dam (on the California/Arizona border) northwestward to the Orocopia Mountains (located near the northeast end of the Salton Sea). The uplifted basement rock consists of ancient Precambrian igneous and metamorphic crystalline rocks; these are abundant in the northern and central portions of the range. Several large exposures of younger Pre-Cretaceous metasediments also occur in the central portion of the range.

These Precambrian and Pre-Cretaceous rocks form the country rock into which the younger Mesozoic granites intrude. Most of these younger granites occur in the northern and central parts of the range. The largest Mesozoic granite pluton (outcrop area: approximately 20 square miles) is located about 10 miles east of Niland. The geology changes as one travels southeastward through the Chocolate Mountains. The southern end of the range is mostly covered by younger Tertiary volcanic rocks. This volcanic field is fairly extensive; the two largest exposures have a total outcrop area of roughly 160 square miles. Most of the area of interest is overlain by these Tertiary volcanic rocks.

PROSPECTING POTENTIAL

Much of the southern portion of the Chocolate Mountains is overlain by Tertiary volcanic rocks. That the area has some mineralization, there is little doubt. The Hess Mine lies near the crest of the southern Chocolate Mountains, about 15 miles east of the Cargo Muchachos. The famous "Potholes" district is located on the southern edge of the Chocolates, about 5 miles south of the Hess Mine.

Prospectors may want to concentrate on the canyons and gulches that drain the southern portion of the Chocolate Mountains. This area lies directly east of the old Tumco/Hedges mining camp. A search for gold-bearing float using a high-quality metal-detector may be productive. Careful mapping and tracing of the float may also be useful in the search for the mine.