It is endemic to headwater tributaries of the Rio Santo Domingo in the Sierra de San Pedro Mártir mountain range of the Peninsular Ranges System, located in Baja California state on the northern Baja California Peninsula.

Biological Survey led explorations into the Mexican mainland (1898) and Baja California Peninsula (1905) to document flora and fauna.

In 1908, preserved specimens of trout that Nelson brought back from the Rio Santo Domingo (Santo Domingo creek) in the Sierra de San Pedro Mártir mountains of Baja California were described by ichthyologist B.W.

[4] In 1989, morphological and genetic studies indicated trout of the Pacific basin were genetically closer to Pacific salmon (Oncorhynchus species) than to the Salmos–brown trout (S. trutta) or Atlantic salmon (S. salar) of the Atlantic basin.

Eschmeyer's Catalog of Fishes recognised Baja California rainbow trout as a species, Oncorhynchus nelsoni Evermann 1908.