A park land swap suggested by Malibu Canyon property owners may be in the making, with Los Angeles County exchanging its 94-acre Tapia Park in Malibu Canyon for the state's 351-acre Placerita Canyon Natural Area Park near Newhall, state and county officials reported. The exchange would make Tapia Park a segment of Malibu Creek State Park, 30 miles west of downtown, and turn Placerita Park, 30 miles northwest of downtown, into a county regional recreation and nature center. State parks planners are studying ways to operate Tapia Park in preparation for taking the swap idea to the state Parks Commission. If the commission approves the exchange, the Legislature and the county Board of Supervisors will also have to approve it. The idea for the swap came from the Monte Nido Valley Property Owners Assn., whose members live in an isolated neighborhood at the north end of Malibu Canyon near Tapia Park. The group has fought for years to limit development in the Santa Monica Mountains.