Free. You can start with nothing.
A single loop out of Marinwood Park and back to it, along some of the highest points in Marin County. A rugged mix of dirt double track fire roads and single track trails along exposed ridgelines, across hilly open grassland meadows and oak woodlands. One aid station, about halfway through.
The race calls the course quite runnable, with a couple of stout long climbs and many short grinder climbs. The big one is the 3 mile, 1500' ascent from Big Rock up the Big Rock Trail to Big Rock Ridge, the second highest point in Marin County. Underfoot it is predominantly dirt fire roads and single track, with some pavement at the beginning and end of the loop.
The Big Alta is a March weekend of trail racing in Marin County, run out of Marinwood Community Center & Park in San Rafael. The 50K goes on the Friday, one loop of 31 miles and 6,700 feet of climbing over Loma Alta and Big Rock Ridge, on fire road and singletrack with the whole Bay Area laid out below. A 28K runs the same ground on the Sunday. Freetrail and Daybreak Racing produce it together, and the name comes off two of the summits the courses cross.
The first Big Alta was run in February 2024 with a 50K and a 28K, and moved to March the following year. In 2026 the event added a point-to-point 100K on the Saturday, which starts at Fort Baker in Sausalito rather than at Marinwood.
| Mile | Station | Cutoff | Crew access | Bag | Pacer | Med | To next |
|---|---|---|---|---|---|---|---|
| 0.00 |
Start - Marinwood Park
NoneSignal wrong?
|
? | ● | ? | ? | ? | ? |
| 8.80 |
Big Rock
NoneSignal wrong?
|
10:45am | ○ | ? | ? | ● | 8.60 |
| 17.40 |
Finish - Marinwood Park
NoneSignal wrong?
|
1:30pm | ● | ? | ? | ? | ? |
11 people have been out there with a camera or a microphone.
+ 3 more.
These are other people's work and we link straight to them. Watching costs nothing and needs no account. More of them: every race we hold, on film.
Nobody sees it until we have read it. No account, no sign-in.
This changes nothing on the page on its own. Somebody checks it against the race first.
Somebody watches it before it goes anywhere near this page. What we are after is footage of this course, on the ground. If it would be just as true of any other race, it is not this.
We want the address of the file the race publishes, not the file. We download it from there so the page can say where the line came from.
We read every one of these and we write back. Every fact here carries the source it came from, and the way a wrong one gets fixed is a person checking it against what you tell us.
Cutoffs move, races get postponed, lotteries open and close. We read the race's own sources and record where every fact came from. Put your email in and we will send you what changed, and where we read it.
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I keep this catalog because the information is scattered and hard to trust. Telling you when it moves is the same job.
