In 1884, Underhill bought the Ontare Ranch in the Santa Ynez Valley from Dixie Thompson for $18,000, moving there with his family.
Two years later, he purchased 5,260 acres south of Los Alamos, California from Dr. James Barron Shaw in spring 1886.
[1] He purchased the 6,000 acre El Roblar Rancho near Los Alamos in 1904, and two years later, he married Carmelita Dibblee (born 1886, Santa Barbara), granddaughter of Pablo de la Guerra and great-granddaughter of José de la Guerra y Noriega.
His most notable achievements include Villa de la Guerra, the Polo Club, Solana (the Peabody residence which eventually became the Center for the Study of Democratic Institutions), and the Roman Pool Pavilion for the George Owen Knapp's Arcady estate (featuring a 40-foot indoor pool encased in an neoclassic structure with a precisely engineered retractable roof).
[3][4] The Underhill estate was used in 1916 as filming location for the movie Purity starring noted artists' model Audrey Munson.