When Miguel Lujan needs gasoline for his truck, he gets it in Carson City, Nev., located 80 miles from his hometown. It’s worth it, the store clerk and the roller-derby player says, to pay one-third less than the local average of nearly $6 a gallon.

California currently has the highest gas prices in the nation, an average of $4.70 a gallon of regular unleaded, according to AAA. Gasoline prices in the U.S. were up 50% in October from the same month last year, amid rising inflation.

The most expensive gas in California is here in Mono County, a 13,000-person tourist destination on the border with Nevada that is home to the Mammoth Mountain ski resort. The average price for a gallon of regular unleaded is $5.66, according to AAA.

In Bridgeport, a town of about 550 that serves as the county seat, the two gas stations were selling regular unleaded for $5.95 and $5.99 a gallon last week. In the nearby town of Lee Vining, which serves as a gateway to Yosemite National Park, a gallon of regular cost $6.09.

Mr. Lujan said he makes the trip to Carson City about three times a week and sometimes takes the bus to save on gas. He fills canisters, routinely keeping about 100 gallons stored in his house.

He started buying gas out of state soon after moving to Mono County four years ago. “The first year I was here, I spent more on gas than anything else,” he said.

President Biden on Wednesday called on the Federal Trade Commission to investigate whether oil-and-gas companies are illegally keeping prices high. Outside analysts were skeptical whether the FTC will find sufficient evidence to substantiate those claims..

California has long had the highest gasoline prices in America. It has the highest tax, at nearly 67 cents a gallon, and only a few aging refineries, which sometimes go offline because of maintenance or other issues, are capable of producing gasoline that meets the state’s standards meant to reduce air pollution.

Though $5.66 represents a new high, inflated gas prices are nothing new in Mono County. Local residents and analysts attribute that to a variety of factors, including its distance from population centers from which deliveries including gasoline come. Sacramento, the closest major city, is about 200 miles northwest.

Even with the high prices, gas stations are able to operate primarily because of tourists who buy gas on their way through, according to Linda Smith, a clerk at the Lee Vining Chevron station.

“They come in and complain,” Ms. Smith said of customers unhappy with the station’s prices. The most common reason she gives, she said, is that it is difficult to operate a business in a remote area that relies on seasonal tourists.

“We’re a pass-through town,” she said.

Station owners in Lee Vining and Bridgeport didn’t respond to requests for comment. Owners of gas-station franchises typically set their own prices based on factors such as wholesale costs, expenses and competition.

Some people stop at the stations in Mono County simply to gawk at the prices.

He had already stopped to take a photo of the station’s price sign on his way into California. This time he bought a soda. “I had heard it was about $5 a gallon. But I was surprised to see it over $6,” he said.