The Sitgreaves Expedition Down the Zuni and Colorado Rivers in 1851 was a combined American scientific and military mission to explore the Zuni River, the Little Colorado River and the Colorado River in 1851. Setting out from northern New Mexico, the expedition traveled west across Arizona and then south along the Colorado to Fort Yuma in California. Mohave native Americans attacked the explorers during their trek across the desert and in a short battle the natives were repulsed.

Lorenzo I. Sitgreaves was a U.S. Army officer from Pennsylvania who led the 1851 Sitgreaves Expedition down the Zuñi and Colorado rivers.