RAIN OR SHINE: A Family Memoir. By Cyra McFadden. Knopf. 177 pp. $16.95.

WALLACE STEGNER once wrote that "the mythic West is the West that everybody knows. Every American child grows up in it." But he added, "The real people of the West are infrequently cowboys and never myths. They live in places like Denver and Salt Lake, Dillon and Boise, American Fork and American Falls, and they confront the real problems of real life in a real region." Rain or Shine is a true story of both the real West and the romantic one. More to the point, it is also a personal inquiry into the relationship between a father and a daughter, a theme with which many of us can identify even if we never lived west of Pittsburgh.

Nearly 10 years ago the author, Cyra McFadden, now a San Francisco Examiner columnist, parodied the hot tub mores of Marin County in a funny piece of fiction called The Serial. Who could have known that her own family would make Marin look drab? Cyra did indeed grow up in the mythic West.

Her father, for whom she was named, was Cy Taillon, the undisputed dean of rodeo announcers, a silver- tongued lady killer with "an alcohol-fueled temper." Her mother was Pat Montgomery, a chorus girl turned trick rider who matched her husband drink for drink, adultery for adultery. In the early 1940s, when rodeos still were carnival sideshows rather than professional sporting events, these two characters rode the circuit from Butte to Baton Rouge in a Packard. Cyra was part of their gypsy existence, sleeping in the car with her parents, playing the slots in the scuzzy bars they used as their living room.

As a child who worshipped her father, she thought of this as the normal American lifestyle. McFadden spins the yarn with the verve of an old buckaroo at a campfire. Her parents were both escaping unpromisiupbringings. Cy came from a hard-working French Canadian family of farmers in North Dakota. Pat hightailed it as fast as she could out of Paragould, Arkansas. They met when they were both working the Montana State Fair, got married after a 24-hour courtship, then took turns charming the world around them while battling each other.

Cyra's arrival hardly altered her parents' spendthrift, irresponsible ways. By the age of three, she had logged 150,000 miles on the road. But several years later, after a terminal fight, Cy and Pat split up. The high- kicking Pat married Roy Qualley, Cy's earthbound gofer, and with Cyra they settled, sort of, in Missoula. Pining for her dashing pa, the little girl found herself under the thumb of a stern stepfather. His "health regime" was only one of his eccentricities: "The main feature was chewing every mouthful of food thirty times to 'get the good out of it . . . ' Roy sat at the head of the dinette-set table, his eyes worried and watchful, and led us out loud in unison chewing. One, two, three, four . . . fourteen, fifteen, sixteen. The leaves changed color while we sat over a single dinner. Snow covered the ground. Spring came, and summer followed by fall again. Or so it seemed to me, rhythmically revolving my jaw."

THE POSTWAR Montana existence McFadden describes bears more than a passing resemblance to a Sam Shepard play. Pat suffered the after-effects of venereal disease. Her Bible-thumping sister Ila Mae moved to Great Falls and wrote weird letters. Cy sidled in and out of his daughter's life like an icon from a Western movie. On one visit, he showed up at her classroom door, "handsome as Gary Cooper, in his whitest hat and nattiest Western shirt and narrow-legged pants, with his beautifully manicured hands resting on a silver and gold belt buckle the size of a salad plate." Still in love, Pat and Cy would smuggle notes to each another through Cyra.

Then Cy married Dorothy, a young woman who had worshipped him from afar since she was 14. Over the years, just as bronc busters gradually made themselves and their rodeos more respectable, so Dorothy domesticated Cy. He stopped carousing, grew famous, announced rodeos on television, lived in a house in Denver that could have belonged to a dentist, voiced right-wing opinions and fathered a pair of rodeo-crazy sons. In the process, he alienated his firstborn. The feeling was mutual; they fought fiercely every time their paths crossed.

Cy died in 1980. Afterward, Cyra made a pilgrimage with one brother to the site of his final rodeo, poignantly trying to mesh childhood memories with contemporary reality. Finally, "wondering if anyone ever makes sense of fathers, or families, and whether their daughters perceive all fathers as part men, part myth," she wrote this extraordinary narrative in an attempt to figure it out. She never does -- none of us does -- but the result is a helluva book.