As the last Ice Age ended and the climate of Southern Arizona warmed and dried out, the flows of the Santa Cruz River near Tucson became erratic and then vanished completely by the mid-1950s due to the construction of a series of cheap hotels on its banks. The native fish of that stretch of the river became extinct, with the exception of the Santa Cruz Sand Trout, which evolved a capability to live in an environment completely devoid of water.

(Salmonis Siliconii)

The Santa Cruz Sand Trout ranges in size from approximately 5 centimeters to over 100 centimeters, and is characterized by a rubbery skin. It is difficult to tell whether a Santa Cruz Sand Trout is dead or alive due to its extremely low metabolism rate.

The Santa Cruz Sand Trout has been commercially harvested and sold in Tucson toy stores for many years, delighting several generations of local children. There are many reports of Santa Cruz Sand Trout escaping Tucson homes and establishing residence in backyard sand boxes and local washes.

The Santa Cruz Sand Trout is one of Baja Arizona's most highly prized sport fish, requiring the use of a 4x4 to troll the riverbed. Beer cans are reportedly the most effective artificial lure to catch Sand Trout.

Efforts to restore the flow of the Santa Cruz River with treated sewage effluent have some environmentalists concerned, as this may cause the destruction of the prime Santa Cruz Sand Trout habitat and lead to their extinction. The Santa Cruz Sand Trout can only survive short periods of wetness, such as occur during the infrequent storm flows in the river. A petition to have the Santa Cruz Sand Trout declared an endangered species is being prepared by the Baja Arizona Ministry of Commercial Fisheries.

The Santa Cruz Sand Trout has also been nominated for an award for water conservation efficiency as it is the only known Arizona species of fish which requires zero gallons per capita of water to survive.