These trout are probably derivatives of the once widespread cutthroat trout. Many of them have evolved brilliant colorations. Most fish in the southwestern desert today live in small streams that are common in the Death Valley System and throughout Arizona and New Mexico. Desert streams are variable and unpredictable, drying during summer to a series of disconnected pools, swelling in a few hours to the flash floods for which the southwest is famous. Flooding is disastrous to fishes and aquatic invertebrates, particularly the smaller ones, battering and isolating them downstream away from their chosen homes or in side pools that evaporate when the flood recedes.
Disaster comes very quickly.
Interestingly, the fishes often balance these flood disasters with immediate spawning. I have seen the Amargosa River teeming with young pupfish two weeks after a flood. Desert stream-dwelling fishes must also adapt to variations of temperature, salinity and dissolved oxygen. Streams in the Death Valley System vary seasonally from 32 to 113 o F. Furthermore, in the summer the water temperature can rise or descend in one day by as much as 45 o F. Salinities can vary from pure fresh water at some stream origins, to more than twice the salt content of seawater downstream and in side pools. Dissolved oxygen concentrations in the water often drop below 1 part per million and can reach zero on hot summer nights in highly productive desert streams.