One Senate seat is up for election in California, held by a Democratic incumbent. Voters will also choose representatives for 53 House seats, 39 of which are held by Democrats and 14 by Republicans. And they will select a governor, an office currently held by a Democrat.
California uses a nonpartisan blanket primary for its state and federal elections (excluding presidential elections). The top two vote-getters across all parties advance to the general election, which means general election opponents can be from the same party. See California’s primary results