At 5 a.m. on Saturday, Dan Williams will toe the starting line of the Western States Endurance Run for the 20th time.

The 61-year-old Lafayette man will jog through Foresthill Divide for the 20th time.

He'll climb through canyons and push through the American River for the 20th time.

But unlike the past 19 runs, Williams will have one of his best running buddies alongside him. Dan's daughter, 26-year-old Christina Williams, will be racing with him this weekend, taking on the rough 100-mile, day-and-night run that has become a part of many ultra-marathoners' lives.

"She's been around it all her life and she got some genetics from me," said Dan, who will be just the third person to do the run 20 times. "It's absolutely amazing. I can't imagine, after all these years I've been running, to be out on the trails with my own daughter."

Dan said it was Christina's idea to take part in the Western States run, which started in 1974.

Runners of all ages start off in Squaw Valley, traverse two canyons, run through Foresthill Divide, cross a portion of American River, follow Auburn Lake trails in darkness and end up at Placer High School in Auburn. Those who can do all that in less than 24 hours earn a silver belt buckle and the official cutoff for a finish is at 30 hours.

Dan noted that even though it's Christina's first time officially participating in the race, she's no rookie. When his daughter was 11, she paced him for the last seven miles of the race. Christina has also been running marathons and 50-mile competitions.

Dan entered his first Western States Endurance Run in 1984 and said that while he used to be able to finish the race in 18 hours when his legs had fewer miles on them, now he's aiming for the 28-hour range. He said loves being out there for the companionship of the trail and enjoys how the run can be an escape from daily life's frustrations.

"There's no worries about money, relationships, jobs — nothing," Dan said. "You just worry about getting to the finish line."

While the Western States Endurance Run is as routine to Williams as brushing his teeth, it's a new world for Albany resident Robert Silva.

Williams gained automatic entry into the race, which uses a lottery system to pick runners, because he's going for the 20th time. Silva's name — much to his surprise — was chosen at random.

Silva, 39, said he had some friends who have done the run, and he qualified, so he figured there would be nothing to lose by entering the lottery. Western States spokesman John Trent said that more than 1,000 people usually register for the race, but only about 400 are given bibs.

"I didn't expect to actually make it," Silva said.

This is the farthest race Silva has ever competed in, he said, though he has ran in a few ultra-marathons up to 50 miles. Silva said he's been training for the race since he found out he made the cut in December. A torn left calf muscle in May slowed his regimen, but he said he feels great and ready to go this weekend.

Silva also been picking the brains of those in his Bay Area-based running group, PanaKids, and Berkeley marathoner Mike Palmer, who is also competing this weekend.

Silva said members of PanaKids will also be there for support, pacing him near the end of the endurance run.

"Those guys are going to drive me and kick my (butt) until I get to the finish line," he said.

One of the toughest things that Silva will encounter this weekend, aside from the heat and elevation changes, will be running through the night. Runners who have competed in the event talked about how hard the last part of the course is, especially since most runners are in motion for more than 24 hours.

David Messman, a 50-year-old Walnut Creek resident, said the final leg of the run is the one that really tests a runners' mettle. Messman is competing in the Western States run for the sixth time, and he's been an ultra-marathon runner for 10 years.

"When you step up to the 100 mile ones, it means darkness and going without sleep through the night," he said. "The sleep depravation, just going though the night, is the biggest challenge."

Lamorinda runners:

Dan Williams, Lafayette

Christina Williams, Lafayette

Robert Cervero, Lafayette

Wally Hasseltine, Lafayette

James Hutson, Lafayette