Both presidential campaigns agree that seven swing states are likely to determine the outcome of this year’s election. California, which has not voted for a Republican in a presidential race since 1988, is not one of them.

But that did not prevent former President Donald J. Trump from heading there anyway on Saturday evening to hold a rally in Coachella, which is better known for its annual music festival with headliners like Lana Del Rey and Bad Bunny than it is for being a stop on a presidential campaign trail.

It was an unusual choice 24 days before the election. In 2020, Mr. Trump lost the state by more than five million votes to President Biden. Four years earlier, Mr. Trump lost the state to Hillary Clinton, who got more than 60 percent of the vote. The last Republican to win the state was George H.W. Bush.

Although Mr. Trump is not expected to be competitive in California, the rally showed that he could turn out a crowd. Throngs of people at Calhoun Ranch, where it was held, braved the desert sun and temperatures that hovered near 100 degrees, with several attendees requiring medical attention for heat-related illnesses.

“I want to give a special hello to Coachella,” Mr. Trump told the crowd, before putting on a red Make America Great Again cap for protection from the desert sun.

Mr. Trump then spoke for about 80 minutes in a rambling speech. He criticized California, Vice President Kamala Harris’s home state, as an incubator of failed liberal policies; disparaged the physical appearance of Representative Adam Schiff, who led the first impeachment trial of him and is now running for Senate; used a crude nickname to refer to the state’s governor, Gavin Newsom; and took a number of detours to praise the billionaire Elon Musk and to criticize President Biden.

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