I'm not in favour of "someone says" estimates... let's try and work it out. According to Wikipedia, it's at about 36 degrees north and has an area of about 7800 square kilometres- 7.8G sq m. If we assume that the daylight averages out as a rough half- sinusoid, the average is about 1/pi times the peak. The solar constant is about 1.4kW per square metre, so the average power per square metre is 1.4cos(36)/pi = 0.36kW/sq metre. That gives about 2800GW average for the whole valley, or about 25 million GWHr annual production. Back to Wikipedia, that has an estimate of 17 million GWHr consumption in the USA in 2005.

Yes, it looks right.. if you cover the whole valley, and conversion efficiency is over 68%.