The Sepúlveda Adobe — usually just called the Yucaipa Adobe — is the oldest structure of its kind in San Bernardino County, a thick-walled, single-storey ranch house built in the early 1840s when the surrounding land was still part of a Mexican land grant. The walls are two-foot-thick adobe brick under a sloping wood-shingle roof; the small rooms inside have packed-dirt floors and the original beam ceilings.
The adobe operates today as a small museum run by the San Bernardino County Museum system. Period furniture, ranching tools, and panels explain Yucaipa's transition from Serrano village to mission outpost to Mexican rancho to American homestead and finally suburb. Visits are by free guided tour, usually only on weekend afternoons — check before driving up. The site is a short detour from the freeway off the western edge of Yucaipa.