El Camino Del Diablo (Spanish for The Devil's Highway) is an historic 250-mile (400 km) road which currently extends through some of the most remote and arid terrain of the Sonoran Desert in Pima County and Yuma County, Arizona. In use for at least 1,000 years, El Camino Del Diablo is believed to have started as a series of footpaths used by desert-dwelling Native Americans. From the 16th to the 19th centuries, the road was used extensively by conquistadores, explorers, missionaries, settlers, miners, and cartographers. Use of the trail declined sharply after the railroad reached Yuma in 1870. In recognition of its historic significance, El Camino Del Diablo was listed on the National Register of Historic Places in 1978.