Six Flags calls Discovery Kingdom "America's only wildlife, marine life and thrill ride park." It says the park has more than 60 rides plus animal shows and experiences. The 135-acre park sits off Interstate 80 in Vallejo. It didn't start there.
Redwood City beginnings
According to Wikipedia, the park opened in 1968 as Marine World, a small zoo in Redwood City. In the mid-1970s it merged with a struggling land-animal park called Africa USA and became Marine World Africa USA. It moved to its current site in Vallejo in 1986, still run by the nonprofit Marine World Foundation.
The city takes over
The park defaulted on its debt to the City of Vallejo, and the city took ownership in 1996. Vallejo then hired Premier Parks, now Six Flags Entertainment Corp., to run and upgrade it. Premier added rides to draw bigger crowds: Popeye's Seaport and the DinoSphere theater in 1997, and the Kong and Boomerang roller coasters in 1998. Kong was moved from Opryland, which had closed. That year the park was renamed The New Marine World Theme Park. It has been part of the Six Flags chain since 1999 and has used several names, including Six Flags Marine World, before becoming Discovery Kingdom.
Getting there without a car
Wikipedia notes that SolTrans buses serve the park Monday through Saturday from Vallejo Station and the Fairfield Transportation Center. Amtrak Thruway Route 7 connects to the Martinez station. A 7.5-megawatt solar canopy over the parking lot, added in 2019, supplies about 80% of the park's energy.
Hours change by season, so check the calendar on the Six Flags website before you go.