SAN DIEGO — Concept: an impromptu Phil Mickelson tour of his native San Diego. Cost: maybe a gallon and change of gasoline. Stops: some golf courses. Tour guides: numerous, accessible, friendly.

Yeah, suddenly Mickelson begins this 121st U.S. Open in his hometown as — whoa! — golf’s most recent major winner, and he begins it up at Torrey Pines, a 23-minute L-shaped drive west on Interstate 8 and north on Interstate 5 from where he grew up.

That would be the Del Cerro neighborhood, an area of hills and sudden vistas and purple flowers in trees and houses comfortable but non-posh, including the one in which Mickelson sprouted, and outside which his father, Phil Sr., a military and commercial pilot by career, constructed that famed 40-yard backyard hole with a green to U.S. Golf Association specifications. It’s a neighborhood where the signage indicates a worthwhile snit over the planned construction of a giant church. (“Save Del Cerro.”)

It’s also where Phil Jr., the year he turned 17, fielded a question from Hank Wesch of the San Diego Union-Tribune about his goals and said, “If I said what they were, people would think they’re far-fetched.” If he had said three Masters titles and one British Open title and two PGA Championships, including one at a record 50 years, 11 months and seven days old, then they weren’t far-fetched.

Here, almost three miles from home and 12-ish miles from the coast, stands Mission Trails Golf Course, 6,000 yards, par 71. It has a front nine in a valley, a back nine on lake shores and “lighted driving ranges with grass hitting stalls,” as it advertises. Don’t bring your coolers or bottles; the sign outside goes, “All Beer Must Be Purchased From The Clubhouse.”

It had the name Navajo Canyon when, as goes the story the senior Mickelson relayed to the San Diego tourism website, the junior Mickelson, about 12, helped out around the course in exchange for hitting and playing privileges. Seemingly everybody has a Mickelson story, and so 34-year-old Paul Rathbun, behind the desk, recalls working at Balboa Park across town when:

“He called me in the pro shop, Balboa, on a Thursday morning, and said, ‘This is Phil Mickelson from the PGA Tour.’

“I said, ‘Of course it is.’

“He said, ‘It is.’

“So I said, ‘I’ve been watching you since I was 12 years old.’”

Rathbun helped arrange a crack-of-morn tee time for Mickelson using Rathbun’s name for cover. “I got to shake his hand and meet him in real life,” he said. “It meant a lot. It was a cool experience. He means a great deal to San Diego.”

Heading westward along Interstate 8, passing the site of the demolished football stadium that calls to mind Doug Williams annihilating the Denver defense in Super Bowl XXII, here’s Riverwalk Golf Course, formerly Stardust, 6,550 yards, par 72.

“DISCOVER YOUR SWING/TEXT A COACH,” a banner on a fence outside reads. With a driving range on the immediate left, the road up the course has its share of errant golf balls come to rest, sometimes amid leaves in gutters. The San Diego Trolley whirs right by on the right. The course boasts its bunkers (nearly 70) and its three lakes and its San Diego River, and schools have let out so that kids are knocking balls, then lugging their hand carts to the clubhouse with aplomb.

This would be the place to which Phil Jr. escaped on Thanksgiving one time, as his sister Tina told Bob Harig of ESPN.com, to have peeved parents hunt him down. It’s near where Mickelson went to University of San Diego High, which changed its name and relocated and gave way to a handsome apartment complex.

On the driving range near the front stand teachers with know-how and Phil stories, including Bob Townsend, whose website reads, “Golf is simple, that’s why it’s so complicated,” and who owns the 82-year-old San Diego Chicken Pie Shop, third-oldest restaurant in San Diego. Townsend went to grades one through eight with various Mickelsons at Blessed Sacrament, where Phils Sr. and Jr. used to win the school’s little tournament. (“It wasn’t even close,” Townsend said.) There are always stories, and just last week came another. One day two men played with the teenage Mickelson, and it went poorly for the latter, so he went to the driving range and spent two hours simply standing behind the ball and then walking to address it, then standing behind the ball and then walking to address it, then standing behind …

“Phil proves that it’s all about the grind,” Townsend said. “‘Cause he’s older. Everybody said he wasn’t going to be a factor anymore. He’s got the arthritis. His swing speed had gone down.” So as Townsend outlined, Mickelson made the changes golf fans know about, and he paired those with the fact he “already had one of the best minds in golf,” and look what just happened last month on the other coast way over there in South Carolina.

“I’ll tell you this,” Townsend said. “People who couldn’t care less about golf know who Phil is in San Diego.”

Native San Diegan Dylan Jackson, assistant club pro at Austin Country Club in Texas, a member of the 2011 Division II national champions with the gloriously named Cal State Monterey Bay, wears a Pink Floyd T-shirt and hits left-handed nearby. “Anybody who’s played golf here growing up has run into him,” Jackson said, and just about anybody who meets Jackson and notices he’s a left-hander from San Diego refers to Mickelson.

Townsend points to another instructor, over there on his knees teaching, and that’s Jason Peterie, and he can tell you from way back that once Mickelson learned to hit a cut in addition to all else, whew, glory did beckon from right up ahead. He also can yank out his phone and show a news clipping from the city match play at Torrey Pines in 1985, with a caption reading, “Jason Peterie upsets Phil Mickelson.” There was that day on the Par 3 course — “That’s where Phil lived,” Townsend said — when Peterie closed with a hole-in-one, a birdie and a hole-in-one, “And Phil’s like, Really?”

Down Interstate 5 and over east a bit, in one of the greatest parks upon all the earth, Balboa, there’s Balboa Park Golf Course, par 72, 6,281 yards, course record by one Sam Snead, a 102-year-old city course with its views of the downtown skyline, Point Loma and the Pacific, and its iconic Tobey’s Diner. (Chalkboard outside: “1/2 Sandwich & Cup of Soup $7.25.”)

Mickelson plays here every once in a while, and, “When he’s here, he stops for everybody — picture, picture, ‘Thank you, thank you,’” said Dan Allen, a golf operations assistant. He brings his smaller “Sunday bag,” and he’s “like [Arnold] Palmer, he makes eye contact with everyone,” Allen said, and then he goes out and plays and eventually exits along a trail to avoid hubbub.

Now he’s playing in a major in his town again, up the road in La Jolla but with a fresh sheen about him, and he said Monday, “What’s happened for me is I spent so many hours [on Torrey Pines] as a kid that, when the course was redesigned, all that local knowledge went away. I really haven’t come out here and spent a ton of time. It’s hard to get a tee time here, and when you do, it’s a long round. So I don’t spend a lot of time out here other than the Farmers [the PGA Tour event in winter].

“I really made an effort here, having the last week off, to spend time out here and really learn, relearn the greens. So I spent a lot of hours out here on the greens last week to see if I can get that local knowledge again, and we’ll see how it goes, but I had a lot of fun kind of relearning and spending a lot of time out here.”

“If he’s in contention this weekend,” Allen said at Balboa Park along the Mickelson tour, “I’ll bet a lot of tee times will open up.”