Marble Canyon Dam was a proposed hydroelectric project on the Colorado River in northern Arizona, planned upstream from the main Grand Canyon as part of broader water-development plans tied to the Central Arizona Project. Envisioned with Bridge Canyon Dam, it was meant to generate power to pump river water toward central and southern Arizona rather than serve chiefly as a stand-alone dam. Engineers studied a moderate thin-arch dam and, at one stage, a far larger diversion scheme that would have greatly reduced river flow through the canyon. Extensive surveys and drilling followed, but unstable limestone geology and political compromise led to the project’s abandonment in the late 1960s, and the area was later protected.