Aug 2, 2011: Images of the world's 10 largest excavations and natural chasms

California's Monticello Dam was built in the 1950s and was designed to provide water for local farms and, in 1983 after the construction of the Monticello Dam Power Plant, power the North Bay area of San Francisco. One of the most notable design features of the dam is the 72m diameter uncontrolled ring gate, or glory hole type spillway - designed to bypass the powerstation.