The claim: Colorado River - Site of former Japanese detention camp (near proving grounds). This site was completely removed in 1990 according to some reports.
What it really is: The most likely internment camp this is being refereed to is the Poston War Relocation Center, which is located in what is now La Paz County (although it had been part of Yuma County until La Paz in 1983).
Several of the buildings there are still in use today, but many others are either deteriorating, or have been removed. Much of the residential areas have also been converted in agricultural use.