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.
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.