62 miles of Marin's greatest hits, from the Golden Gate to the finish line
The Big Alta 100K takes place on March 20, 2027 in San Rafael, CA.
The Big Alta 100K is 62 miles with 12,640 ft of elevation gain.
No — The Big Alta 100K uses open registration; no lottery is required.
Yes, crew is allowed at The Big Alta 100K. Crew can access 6 of the 11 locations listed on this page.
No, pacers are not allowed at The Big Alta 100K.
Yes, The Big Alta 100K allows drop bags. Drop bags are accepted at 4 of the 11 locations listed on this page.
The Big Alta 100K has 9 aid stations along the course.
The overall cutoff for The Big Alta 100K is 17h. Individual cutoffs for 5 of the 11 locations listed on this page are published below.
The Big Alta 100K has published cutoff times at 5 points on the course. Each one is listed on this page with its location, distance and cutoff.
Other trail races within 100 miles
The Big Alta 100K is a world-class point-to-point trail race traversing the entire length of Marin County from Fort Baker near the Golden Gate Bridge to the finish at Marinwood Community Center. The course strings together Marin's greatest scenic landmarks — Fort Baker, Marin Headlands, Stinson Beach, Mount Tamalpais, Lagunitas Lake, Pine Mountain, Loma Alta, and Big Rock Ridge — into 62 miles of varied terrain including singletrack, fire roads, and exposed ridgelines. With 12,750 feet of climbing and a 17-hour cutoff, the race demands endurance and navigation savvy, with a mandatory GPS device required throughout due to high trail use in this National Parks Service-permitted region.
Experienced ultrarunners
San Rafael, CA, United StatesMarch 20, 2027
The Big Alta 100K is a point-to-point trail race in San Rafael, CA, United States, held on March 20, 2027. The course covers 62 miles, climbs 12,640 ft, and has a 17h cutoff.
| Location | Mile | Elevation | Cutoff | Crew | Drop bags |
|---|---|---|---|---|---|
START - Fort Baker Start | 0.0 | 16 ft | — | Crew | |
AS1 - Rodeo Beach Aid Station | 6.5 | 26 ft | — | Crew | |
AS2 - Muir Beach Aid Station | 12.3 | 13 ft | — | Drop Bags | |
AS3 - Cardiac Hill Aid Station | 19.2 | 1,365 ft | — | ||
AS4 - Stinson Aid Station | 22.1 | 52 ft | 6h12:00 PM | Crew | Drop Bags |
AS5 - Tam Summit Aid Station | 30.1 | 2,343 ft | — | ||
AS6 - Lagunitas Aid Station | 35.6 | 728 ft | 10h4:00 PM | Crew | Drop Bags |
AS7 - Azalea Hill Aid Station | 38.8 | 1,083 ft | — | ||
AS8 - Fox Hollow Aid Station | 47.9 | 259 ft | 13h7:00 PM | Crew | Drop Bags |
AS9 - Big Rock Aid Station | 52.6 | 656 ft | 14h30m8:30 PM | ||
FINISH - Marinwood Community Ctr Finish | 61.2 | 79 ft | 17h11:00 PM | Crew |
Aid station details for this race are still being filled in. Cutoffs and access rules come from the race’s own published information and can change — check the official race details before planning around them.
Sign in for race-day weather at every station, points of interest, segment-by-segment analysis, pacing, and to save this race to your calendar.
Friendly, leashed dogs are allowed at the event staging area and finish line, but not on the race course.
Late March in coastal Marin County brings classic Northern California spring variability. Morning temperatures typically start in the 40s°F and climb to 55-75°F by afternoon. Marine fog and coastal overcast are common early in the day near Rodeo Beach, Muir Beach, and Stinson Beach. Spring weather is famously unpredictable — sun, wind, fog, and rain showers can all occur within a single day. The 17-hour cutoff means many finishers will be running in darkness, with evening temperatures dropping back to the 40s°F. Come prepared for the full range of coastal spring conditions.
Coastal Marin spring weather can include sun, wind, fog, and rain showers all in one day
Runners finishing near the 11PM cutoff will experience cold, dark conditions with temperatures dropping to the 40s°F
Exposed ridgelines on Marin Headlands, Mt. Tamalpais summit, and Big Rock Ridge can experience strong winds
Spring rainy season — mandatory gear policy may be activated if rain is forecast race week
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