It is endemic to southern California, where it is now known only from a few areas on the heavily developed coastline of Los Angeles and Ventura counties.

At one point in time there were 43 populations of P. lyonii distributed among the Santa Monica Mountains, Simi Valley, Palos Verdes Peninsula and Catalina Island.

In a 2006 search only 21 Pentacheata populations could be located, with occurrences on the Palos Verdes Peninsula having long been deemed extirpated.

Populations on Catalina Island were thought to be extirpated until 112 individuals were re-discovered in 2011 on a ridgeline near Two Harbors.

The most recent area suspected of extirpation is Stunt Ranch where no flowering individuals have been seen since 1990, after an 8-year population decline.