The Golden State's primary rules — selecting the top two vote-getters regardless of party affiliation — produced a stampede of candidates in several key districts.

As of Wednesday morning, several of those races were too close to call, and it may take several days to tabulate absentee ballots for a final count.

10th District: Democrats are hoping to unseat four-term incumbent GOP Rep. Jeff Denham, who faced little opposition in his bid for his party's nomination. Among Democrats, technology investor Josh Harder was leading in the race for the second slot, but Republican Ted Howze, who ran on virtually no campaign budget, was within a point of edging him out. Harder has raised more than a million dollars from outside the district. Democrat Michael Eggman, a small businessman who lost to Denham by about 3 percentage points in 2016, was trailing in his bid for a second spot on the ballot.

21st District: Democrats have also targeted incumbent Republican David Valadao in this midstate district, which went for Democrat Hillary Clinton in the 2016 presidential election. Valadao will face T.J. Cox, an engineer and businessman, on the November ballot. Out-of-district Republicans have donated more than half a million dollars to Valadao's campaign, or about a quarter of his total war chest

25th District: Long-distance Democratic donors have invested heavily in nonprofit executive Katie Hill's bid to unseat incumbent GOP Rep. Steve Knight. That funding lead for Hill appears to be paying off at the ballot box. As of Wednesday morning she was holding onto a second place finish ahead of Democrats Bryan Caforio, a lawyer, and Jess Phoenix, a geologist.