A federal survey of Rancho Muscupiabe in 1867 provided legal land description of 12,204 ha (30,145 acres) in San Bernardino Valley, southern California, which fortuitously includes records of prominent native vegetation marking the location of survey stations along the land grant boundary. We matched legal land descriptions to the mapped vegetation occurrences, documented before agricultural land use and urbanization cleared the land, to relocate site-specific species localities in 1867 for comparison to historical botanical collections and extant distributions. We show that Juniperus californica, a desert conifer uncommon in cismontane regions of southern California, occurred at Del Rosa near Little Sand Creek on the northern boundary of Rancho Muscupiabe, which extends the historical species range from nearest extant occurrences on alluvial terraces along the Santa Ana River Wash (7 km SE) and Cajon Creek (13 km W). Vegetation records accompanying the 1867 survey also document the endemic Juglans californica at Devil Canyon in the San Bernardino Mountains, and at the SE base of San Sevaine Ridge in the San Gabriel Mountains. The 1867 survey map predates earliest recorded botanical collections in San Bernardino County of Juniperus californica (JEPS48231) and Juglans californica (POM123336) by 15 yr. A synthesis of historical and modern data is presented to build upon comprehensive atlases of California vegetation and show that the easternmost distribution of Juglans californica extends along the cismontane foothills of the San Bernardino Mountains to Millard Canyon near Banning Pass.