The park served as a tuberculosis sanatorium from 1918 - 1969 and housed a sizable hospital complex, including a sunroom designed by architect Julia Morgan, famed for her design work on Hearst Castle. (The park's website includes a variety of photos of the sanatorium buildings and patients.)
The hospital buildings, alas, didn't receive the same level of loving attention that Hearst Castle has, gradually falling into disrepair, and most of them had to be chopped down before the park could open. The largest remaining sanatorium-era building is a venerable barn in the south end of the park. While the barn lacks famous-architect chops, it's still picturesque, particularly from the west (the east face includes an electrical junction box that tends to compromise the rustic air unless you can mentally photoshop it away).