Three Kids Mine site, Nevada

Off Lake Mead Parkway (State Route 564) on the way to Lake Mead from Henderson, almost across the street from the turnoff to Lake Las Vegas. This was a major manganese deposit that was worked until 1961, when the government-subsidized price ran out. The mill was then dismantled shortly thereafter. Minor byproduct Pb, Cu, Ag, and Au were also recovered. If you click the "hybrid" view on the location and back out a few notches, you can see some big open pits to the south.

A drilling program in 1959 located lots of additional manganese ore. It probably won't get mined in this cycle of civilization, however! I can just imagine what the residents in a place as ritzy as Lake Las Vegas would think of a manganese mine in their backyard...