The power flows from a mix of solar panels and hydroelectric turbines including the Hoover Dam.
It seems odd to think about hydroelectric power in a desert as a renewable resource, but it does come from snow in Colorado.
http://www.ibtimes.com/lake-mead-water-level-drops-record-lo...
[1] https://en.wikipedia.org/wiki/Colorado_River_Compact [2] https://www.brookings.edu/blog/planetpolicy/2015/05/02/5-fac...
[1] https://en.wikipedia.org/wiki/Prior-appropriation_water_righ...