The Burdell Frame House is a two-story clapboard structure built in 1874 for Mary Burdell’s cousin, Mary Joynsen. Originally a rectangular building, it was later modified with a projecting two-story addition on the end facing the parking lot, a two-story shed on the opposite end, and a single-story garage at the rear. Along with the mansion, its interior was altered into a dormitory facility when Rancho Olompali was acquired by the University of San Francisco for use as a retreat. A large glass conservatory, or greenhouse, once stood downslope from the house, and a swimming pool and bath house occupied the site in the 1950s. Part of the building now houses the park Visitor Center and Administration Office.