The Spaniards had called it Vallecitos (for Little Valley). Sovereign Peter Larsen from Norway homesteaded there in the early 1870s. James Peebles Marshall (JPM) Rainbow, a settler who came from Pennsylvania in 1875, and began acquiring much of the land in the valley. About 1887 JPM Rainbow & W.J. Gould formed a land company and purchased Larsen’s homestead. They surveyed and subdivided the property into lots and filed a townsite map with the San Diego County Recorder office.
The town makers initially suggested the Post office be named for Larsen, the first homesteader. But Larsen said no and recommended “Rainbow” as a better name as it is a word having more meaning. The Rainbow Post Office was established about 1888 and kept in the Rainbow General Store, which stood near the present day southwest corner of Fifth and Rainbow Valley Blvd.
JPM Rainbow was a successful fruit farmer. He was elected to the San Diego County Board of Supervisors for two terms. However, when Riverside County was created and carved out of northern San Diego County in 1893, the county line ran through his property, leaving his barn in San Diego County and his home in the new Riverside County. JPM Rainbow resigned his seat on the San Diego County Board of Supervisors saying that he had no intention of living in his barn.
JPM Rainbow died in 1907 at the age of 71.
Tom Frew, Historical Society historian