It was just like any other late weekend night for Martin Guzman, the owner of Taqueria Los Coyotes, with scores of drunken 20-somethings buying burritos.

Little did he know on that October night that one of these coolsters was about to introduce a recipe that might very well change how San Francisco sees burritos.

The young man from San Diego asked for a California burrito.

“I told him to show me how to make it and he did,” Guzman recalled. “It has french fries, carne asada, guacamole, sour cream, cheese.”

Since then Guzman has adopted the California burrito, which has its roots in San Diego County, where it is a staple of Mexican food. It now makes up 20 percent of his sales, he said.

He added that young college students — the majority of those who buy it come from all over San Francisco to get the California burrito, which he advertises through banners at the restaurant and word of mouth.

“Before I used to buy one box of fries for two weeks, now I buy 10 boxes for one week,” he said. “The distributor asked me ‘Do you sell hamburgers?’ No, just California burritos.”

He’s not the only one: Last month Tortas Boos Voni in the Excelsior District introduced the California Burrito to its menu. They take a healthier approach, replacing the french fries with cooked potatoes.

The appearance of the California burrito in San Francisco’s Mexican restaurants isn’t surprising to the city’s many San Diego transplants. Any influx of people from a different region brings with it their traditions and food — the very phenomenon that has made Mexican food so prevalent in California.

In recent years, the number of students coming to San Francisco from Southern California, where the California burrito is widespread, has been on the rise. San Francisco State University, for example, has had a 21 percent increase in students from San Diego, from 839 in 2005 to 1,075 in 2009, according to university records.

The number of students from Los Angeles has increased by 25 percent, from 1,340 to 1,805, and students from Orange County have increased by 32 percent, from 658 to 970. Meanwhile, students from San Francisco have decreased by 15 percent, from 5,987 to 4,987.

It hasn’t stopped with burritos. While researching the California burrito, Guzman came across carne asada fries, another Southern California staple. Restaurants like Olivos in the Tenderloin have recently begin serving carne asada fries — essentially the California burrito minus the tortilla.

Guzman, who has owned his restaurant since 2004, said he’s just following the market and is considering introducing guacamole fries — a plate of fries topped with melted cheddar cheese and guacamole.

“I am a person who listens to their customers,” he said.

(Full disclosure: The author was raised in San Diego County and attended San Francisco State University.)