1931 Map of Moon Mtn

About this map

The Colorado River Indian Reservation dominates the western landscape of this early 20th-century survey, where the Colorado River serves as the natural boundary between Riverside County, California, and Yuma County, Arizona. This desert terrain is defined by the sharp elevations of the Dome Rock Mountains and the distinct peak of Moon Mtn. The map documents a period of active mineral exploration in the region, specifically marking the Valenzuella Mine and the Mammoth Mine along the western slopes of the range. To the east, the topography transitions into the expansive La Posa Plain, a broad drainage basin fed by ephemeral watercourses such as Tyson Wash. The absence of developed roads or settlements highlights the isolation of this mining and reservation land prior to the mid-century expansion of local infrastructure.