⏵ Course guide · Marin County race weekend
The Big Alta packs three separate races into one Marin County weekend: a 50K on Friday, a new point-to-point 100K on Saturday, and a 28K on Sunday, all summiting some of the county's highest points with views across the entire San Francisco Bay Area. I will walk you through the three-day format first, then give you a pacing and fueling plan for coastal Nor Cal climbing. There are free calculators along the way to dial in your own numbers.
These facts come from the official Daybreak Racing event page. Check the current year details, cutoffs, and aid stations before you commit. Race logistics change year to year.
Every Big Alta distance summits some of Marin County's highest points, with event namesakes Loma Alta and Big Rock Ridge among the landmarks on course. This is a race built around elevation you can see from the trail rather than a published vert number.
The weekend opens with a single-loop 50K starting and finishing at Marinwood Community Center & Park. It sets the tone for the weekend: real Marin climbing rewarded with seemingly endless Bay Area views from the ridgelines.
The marquee event is new for this era of the race: a point-to-point 100K starting at Fort Baker, near the Golden Gate, and finishing back at Marinwood. Runners take a shuttle bus from Marinwood to the Fort Baker start line at 5:00 AM, since parking and leaving a car at the start is not permitted. The 2027 edition is a Western States Qualifier. Because the region sees heavy social-trail use, all 100K runners are required to carry the course GPX file loaded onto a GPS watch or navigation app, not rely on course markings alone.
The weekend closes with a single-loop 28K, shorter than the other two distances but built on the same demanding Marin terrain. It is a fitting closer for anyone who ran Friday and Saturday too, or a standalone entry point into the weekend for a first Big Alta finish.
Daybreak Racing does not publish total elevation gain for any Big Alta distance, so build your pacing plan around the cutoffs and the terrain description rather than a vert figure that does not exist yet.
The 28K gives you 5.5 hours, the 50K gives you 9, and the 100K gives you 17 hours from a 6 AM start. None of these are tight for a well-prepared runner, which tells you Daybreak built this course to be finished by a well-paced field, not just survived by the fastest. A grade-adjusted pace target for the climbs on Loma Alta and Big Rock Ridge gives you an honest number to hold, especially on the 100K where a slow first half can eat the back half of your day.
Runners tackling all three days should treat Friday's 50K and Sunday's 28K as bookends to Saturday's 100K, not separate hard efforts. Go out conservative on the 50K specifically to protect Saturday, and expect Sunday's 28K to feel harder than its distance suggests on legs that already have two big days in them.
⏵ Free tools to pace this course
Late March on the Marin coast can deliver sun, wind, fog, and rain in the same day, so your fueling and layering plan needs to flex, especially across a multi-day weekend.
Aim for roughly 60 to 90 grams of carbohydrate per hour on the 50K and 100K, and sodium in the 300 to 700 mg per liter range, leaning higher if the day turns warm and sunny rather than the more typical cool and breezy coastal pattern. The 28K on Sunday is short enough that consistent aid-station access matters more than a precise per-hour plan.
With up to 17 hours on course and a 6 AM start, 100K runners should plan fueling into the evening and carry layers for temperature drops after dark. Aid stations along the point-to-point route are your resupply points; use them deliberately rather than guessing at what you can carry from Fort Baker to the finish.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and a changeable Marin County weekend with the free ultra fueling calculator. Browse the rest of the free running tools at the tools hub.
⏵ Train for it with Summit Line
Get a race-day plan built around YOUR fitness, this Marin County climbing profile, and your projected splits. Summit Line reads your real training, builds a plan for a multi-day mountain weekend, and rehearses your fueling so race day is something you execute, not guess at.
Daybreak Racing does not publish a total elevation gain figure for any of the three Big Alta distances, but all three courses summit many of the highest points in Marin County, including Loma Alta and Big Rock Ridge, with views stretching across the entire San Francisco Bay Area. The new 100K on Saturday is the marquee test, a point-to-point course starting at Fort Baker with an 11:00 PM cutoff, 17 hours after its 6:00 AM start. Without a published vert number, treat the generous cutoffs as your honest read on difficulty: this is built as a big mountain day in Marin, not a fast course.
The Big Alta runs three separate races across three days. Friday is a single-loop 50K, Saturday is a new point-to-point 100K starting at Fort Baker, and Sunday is a single-loop 28K. You can run one, two, or all three, and each has its own field cap and cutoff.
For the 50K and 28K, plan a standard ultra fueling window: roughly 60 to 90 grams of carbohydrate per hour and 300 to 700 mg of sodium per liter, adjusted for late March coastal Nor Cal weather that can swing from sun to fog to rain in a single day. The 100K is the bigger commitment, up to 17 hours on course from a 6 AM start, so plan for a full day of eating, likely into the evening, and carry course-appropriate layers since Marin weather this time of year is genuinely unpredictable. Build your numbers with the free ultra fueling calculator before race day.
The 50K has a 9 hour window, 7:00 AM start to a 4:00 PM finish cutoff. The 100K has the most room, 17 hours from its 6:00 AM Fort Baker start to an 11:00 PM final cutoff. The 28K has the tightest window at 5.5 hours, from an 8:00 AM start to a 1:30 PM cutoff. If you are running multiple distances across the weekend, respect how each day compounds fatigue into the next.
All three courses summit some of Marin County's highest points, including Loma Alta and Big Rock Ridge, with sweeping views across the San Francisco Bay Area. Expect coastal Northern California trail: exposed ridgelines, wooded singletrack, and genuinely changeable late March weather, daytime highs generally 55 to 75°F and morning lows in the 40s, with sun, wind, fog, and rain all possible in the same day. The 100K requires runners to carry the course GPX file on a GPS watch or phone nav app, since the region sees heavy social-trail use and course markings alone are not a reliable reference.
The 28K and 50K are reasonable entry points if you have some trail experience and are comfortable with real Marin County climbing, even without a published vert number to plan against. The 100K is the harder call: it is brand new for 2027, point-to-point, starts at a separate venue reached by shuttle, and is a Western States Qualifier, all signals that it is built for runners who already have ultra finishes behind them. If you are newer to the distance, the Friday 50K or Sunday 28K, run on their own or as part of the full weekend, are the more honest starting point.
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<a href="https://runsummitline.com/guides/the-big-alta">The The Big Alta course guide</a>This guide is independent and for planning only. The course details, dates, cutoffs, and aid stations come from public sources and can change year to year, so confirm the current specifics with the official race before you register or run. The fueling and pacing advice is general and not medical advice.