The Hyatt Grand Champions took out there grass courts and replaced them with a spa. There are grass courts at La Quinta, the JW Marriott Desert Springs resort, and Mission Hills in greater Palm Springs and, as another poster pointed out, at La Costa in Carlsbad. Last I checked those at the JW Marriott were open to people staying outside the resort. You can get more information about all these resorts by visiting
http://travel.tennis-warehouse.com