1 year after people; As long as the pipes are open, which carry water to cool the generators that power Las Vegas, the Hoover Dam will still be supplying electricity. But now these generators are about to be brought down by an organism the size of a thumb nail...the Quagga Mussel. These organisms will place on the inside of a pipe, multiply on top of one another, and eventually completely block the diameter of the pipe, preventing cooling water from moving to a generator, and causing the generators to overheat and shut down. Las Vegas now goes dark permanently. With the generators down no water moves through the dam and the Colorado River downstream will run dry until the waters rise high enough in Lake Mead to run through the dam’s spillways like a waterfall.
10,000 years after people; The Hoover Dam, one of the last remnants of modern civilization, finally collapses due to erosion of its concrete and the cumulative effect of seismic activity.