San Rafael, California · Trail
Official site ↗The Big Alta
A March weekend in Marin County over three days: a 100K point to point from Fort Baker with 12,750 feet of climbing, and a 31-mile loop out of Marinwood Park with 6,700.
Distances
100K
- Distance
- 62.5 mi (101 km)
- Vert gain
- 12,750 ft (3,900 m)
- Start
- 6:00 AM GMT-7
- Cutoff
- 17 hr
Saturday. Mass start at Fort Baker, no waves and no announcements, point to point to Marinwood Park; the finish closes at 11:00 p.m.
50K
- Distance
- 31 mi (50 km)
- Vert gain
- 6,700 ft (2,000 m)
- Start
- 7:00 AM GMT-7
- Cutoff
- 9 hr
Friday. Single mass start at Marinwood Park, no waves; the finish closes at 4:00 p.m. On-course cutoffs 11:00 a.m. at mile 14.3 and 1:30 p.m. at 23.2, with a soft one at 9:25 a.m. at 9.4
| Distance | Vert gain | Start | Cutoff | Notes |
|---|---|---|---|---|
| 62.5 mi (101 km) | 12,750 ft (3,900 m) | 6:00 AM GMT-7 | 17 hr | Saturday. Mass start at Fort Baker, no waves and no announcements, point to point to Marinwood Park; the finish closes at 11:00 p.m. |
| 31 mi (50 km) | 6,700 ft (2,000 m) | 7:00 AM GMT-7 | 9 hr | Friday. Single mass start at Marinwood Park, no waves; the finish closes at 4:00 p.m. On-course cutoffs 11:00 a.m. at mile 14.3 and 1:30 p.m. at 23.2, with a soft one at 9:25 a.m. at 9.4 |
About
The Big Alta is run in Marin County, immediately north of San Francisco, by Daybreak Racing and Freetrail together. The weekend spans three days and three distances: the 50K on the Friday, the 100K on the Saturday and a 28K on the Sunday. The name comes from two course landmarks, Loma Alta and Big Rock Ridge.
The 100K is the bigger race and the newer one. It runs point to point from Fort Baker at the north foot of the Golden Gate Bridge, through the Marin Headlands, Stinson Beach, Mount Tamalpais, Lagunitas Lake, Pine Mountain and Loma Alta, and finishes at Marinwood Park: 62 miles and 12,750 feet of climbing. The race calls the permits behind it one of its own greatest accomplishments.
The 50K is a single loop from Marinwood Park over the same ridgelines, 31 miles with 6,700 feet of climbing.
Course
Both courses mix fire road and singletrack over open grassland, ridgeline and woodland, and both summit several of the highest points in Marin County. The 50K has three aid stations and the 100K has more; crews are allowed only at named aid stations and at the start and finish.
The 100K requires the course GPX file loaded on a watch or a phone navigation app, because the region is heavily used and course markings can be moved. There is no race-morning bib pickup for the 100K at all.
How to register
Open sign-up on UltraSignup, with no lottery: "There is no lottery for any races." The 100K is capped at 400 places and the 50K and 28K at 300 each, and the race says each one sells out earlier every year. Bib transfers to another person are not allowed. Entry for 2027 opens on September 14, 2026, priced in two windows: the 100K at $310 then $340, the 50K at $180 then $205, and the 28K at $140 then $160. The race also says the 2027 100K "will become a WSER Qualifier", which the official list does not yet carry.
Results by year
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