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Green rolling hills and oak woodland in Sonoma County, with dry grass in front
Ashe Walker / Unsplash

Lake Sonoma 100K and 50K course maps and aid stations

A spring ultra on the singletrack around Lake Sonoma, in the wine country hills outside Healdsburg.

April 8 to 11, 2027 Healdsburg, California

Lake Sonoma started in 2008 as a 50 miler, and UltraRunning magazine has called its field one of the most competitive in the US. Since 2026 the April weekend has been a 100K, a 50K and the Trail Sisters Half Marathon, a women's race, all on Saturday. The original 50 Mile moved to October and is now part of Aravaipa Running's Sonoma Fall Classic, a separate event on October 17 and 18, 2026.

The 100K and 50K start and finish at the Lake Sonoma Visitor Center, just below Warm Springs Dam, and the half starts at Lone Rock. The organizer says the trails are nearly 95 percent singletrack over relentless rolling hills, and they cross creeks more than a dozen times. The 100K also runs through groves of madrone.

The race warns that cell service around the lake is "spotty at best with no service in many areas", and there's none at Warm Springs. Download the course map before you drive out: your phone's GPS shows where you are without a signal.

This is an unofficial guide: Goat Maps isn't affiliated with Lake Sonoma 100K, 50K and Trail Sisters Half Marathon. Check the official site before you enter or race.

Lake Sonoma course map

Every course's aid stations on the Goat Maps topo map. Each course has a map of its own further down.

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Save it in Goat Maps for a recce or race day. GPS shows where you are even without a signal.

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Lake Sonoma courses

CourseDistanceClimbingStartTime limit
100K62.1 mi (100 km)15,000 ft (4,572 m)Sat, Apr 10, 5:00 AM19 h
50K31.1 mi (50 km)5,700 ft (1,737 m)Sat, Apr 10, 7:30 AM11 h
Trail Sisters Half Marathon13.1 mi (21 km)2,339 ft (713 m)Sat, Apr 10, 9:30 AM5 h

Lake Sonoma 100K

A climb of Pritchett Peak at sunrise, then out and back on the original 50 mile course to Lone Rock.

Distance
62.1 mi (100 km)
Climbing
15,000 ft (4,572 m)
Start
Sat, Apr 10, 5:00 AM
Time limit
19 h

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The 100K opens with a climb up Pritchett Peak, with a water stop at the top, then drops back toward the Visitor Center and climbs again to the South Lake Trailhead. From there it runs the original Lake Sonoma course out to Lone Rock and back. The course page gives 15,000 feet of climbing over 62.1 miles.

The longest gap is 6.9 miles between Island View and Warm Springs, and you run it both ways. Pritchett, South Lake and Wulfow have water only. You need a headlamp if you leave Warm Springs after 3:30 PM. If you have to drop, do it at Warm Springs, Liberty Glen or Lone Rock: Island View and Wulfow are hard to reach and have no one to drive you back. The race brings Island View's supplies in by boat and carries them up the hill.

aid stations

miWhereCutoff
0Lake Sonoma Visitor Center (start and finish)
5.8Pritchett Peak (water only)
11.4Woodridge Drop bag
12.7South Lake Trailhead (water only) Crew
17.3Island View
24.2Warm Springs Crew, Drop bagSat 12:30 PM
29.6Wulfow (water only)
32.3Liberty Glen Crew, Drop bag
36.6Lone Rock Sat 4:15 PM
40.9Liberty Glen Crew, Drop bag
43.6Wulfow (water only)
49Warm Springs Crew, Drop bagSat 8:00 PM
55.9Island View Sat 10:00 PM
60.5South Lake Trailhead (water only)
62.1Lake Sonoma Visitor Center (start and finish) Midnight
A dirt trail winding through grass and oaks toward green hills in Sonoma County
Ashe Walker / Unsplash

Lake Sonoma 50K

Singletrack around the lake to Warm Springs and back over the bridge to the finish.

Distance
31.1 mi (50 km)
Climbing
5,700 ft (1,737 m)
Start
Sat, Apr 10, 7:30 AM
Time limit
11 h

Take this course offline

Download its map in Goat Maps and you can find the next aid station without a signal.

Open in web map

The 50K starts on the grass beside the Visitor Center and runs a short stretch of road to spread the field before the singletrack. It passes South Lake, Island View, Warm Springs, Wulfow, Liberty Glen and Bummer, then crosses the bridge over the lake. Save something for the end: the organizer calls the last few miles a "screaming downhill" to the finish.

The course page gives 5,700 feet of climbing. Island View to Warm Springs is the long gap again, 6.9 miles, and South Lake and Wulfow are water only.

A calm lake near the town of Sonoma, with autumn trees on a point and people fishing from the shore
Richard McDavid / Unsplash

Lake Sonoma Trail Sisters Half Marathon

A women's half from Lone Rock, out to Oak Knoll and back, then over the lake bridge to the finish.

Distance
13.1 mi (21 km)
Climbing
2,339 ft (713 m)
Start
Sat, Apr 10, 9:30 AM
Time limit
5 h

Take this course offline

Download its map in Goat Maps and you can find the next aid station without a signal.

Open in web map

The Trail Sisters Half is a women's race, and the rules welcome non-binary runners too. It starts at the archery range by the Lone Rock trailhead, goes out to Oak Knoll and back, then crosses the bridge over the lake to finish at the Visitor Center. Expect 2,339 feet of climbing. You have 5 hours, and the cutoff at Archery is 12:00 PM.

If you think you won't finish, drop at Archery: Bummer is hard to reach. Park at the Lone Rock lot; a free shuttle runs from the finish back to the start from 12:30 to 3:30 PM, and the race takes a finish line drop bag from the start to the finish for you.

A lone tree on dry grass in the Sonoma County hills, with forested ridges and clouds behind
Danilo Lessa Bernardineli / Unsplash

Registration and fees

Entry is on UltraSignup, and it closes Friday, April 9, 2027 at 11:59 PM Pacific. The fee rises in steps: the 100K is $250 through October 31, $280 through January 31 and $300 after; the 50K $165, $185 and $200; the half $95, $110 and $115. Processing fees and taxes are extra. A few elite entries for the 100K and 50K go through a questionnaire on the race site.

There are no deferrals (other than for pregnancy), credits or transfers. Cancel by December 31 and you get half the race fee back. You can move down a distance until April 1.

Getting to Lake Sonoma

Vineyard rows on a sunny hillside below a wooded ridge near Sonoma
Spencer DeMera / Unsplash

From Healdsburg it's 10 miles out Dry Creek Road to the lake. San Francisco International is 94 miles away, about two hours by car, and Sacramento International 128 miles, about two and a half. Pick up your packet on Thursday or Friday at Healdsburg Running Company, or at the start on race morning.

The 100K and 50K park in the two Visitor Center lots, and the half at Lone Rock. You can camp next to the start and finish on Friday and Saturday nights without a reservation, in a vehicle that fits a standard parking space (no trailers) or a tent in the marked area.

Crew and drop bags

100K crews can meet runners at the South Lake Trailhead on the way out, and at Warm Springs and Liberty Glen both ways. 50K crews can go only to Liberty Glen, in Group Lot E of the campground. The race asks 100K crews to be at South Lake by 6:30 AM to free up space at the Visitor Center for the 50K.

Warm Springs is about 45 minutes from the start on a slow, winding road; you park at a gate and walk the last half mile. Print the crew driving directions, since your phone may not work, and arrive with a full tank of gas.

100K drop bags go to Woodridge, Warm Springs and Liberty Glen, and 50K bags to Warm Springs and Liberty Glen. Bags must be smaller than a shoe box and in by 4:45 AM for the 100K and 7:15 AM for the 50K.

Weather and what to carry

A lone tree on dry grass in the Sonoma County hills, with forested ridges and clouds behind
Danilo Lessa Bernardineli / Unsplash

In Healdsburg, April averages a high of 72°F and a low of 45°F, with 2.87 inches of rain over the month, by NOAA's 1991 to 2020 normals. If it's warm, the race says you'll likely need more than one bottle in the afternoon.

Aid stations have no cups, so every runner carries at least one bottle, flask or bladder. Poles aren't allowed. Bring any gels or drink mix you rely on, since the stations stock Skratch and a mix of sweet and savory food.

Lake Sonoma aid stations and GPS coordinates

For crews and spectators: each place on the map in decimal degrees, latitude first. Paste them into any map app or add them as waypoints in Goat Maps.

  • Lake Sonoma Visitor Center (start and finish)

    38.71791, -122.99795

  • Archery, Lone Rock (half marathon start)

    38.71507, -123.04572

  • Pritchett Peak (water only)

    38.74821, -123.04954

  • Woodridge

    38.71585, -123.00028

  • South Lake Trailhead (water only)

    38.70727, -123.00895

  • Island View

    38.68911, -123.02410

  • Warm Springs

    38.70338, -123.08611

  • Wulfow (water only)

    38.71123, -123.05962

  • Liberty Glen

    38.71063, -123.05335

  • Lone Rock

    38.71385, -123.04489

  • Bummer

    38.70901, -123.03245

  • Oak Knoll

    38.72556, -123.03850

Lake Sonoma FAQ

When is Lake Sonoma 2027?

Saturday, April 10, 2027. The 100K starts at 5:00 AM, the 50K at 7:30 AM and the Trail Sisters Half at 9:30 AM. Packet pickup is on the Thursday and Friday in Healdsburg, and there is a thank-you social with wine tasting on the Sunday.

Is the Lake Sonoma 100K a Western States qualifier?

Yes. Western States lists the 2027 Lake Sonoma 100K as a qualifier for its 2028 lottery, with a 19 hour standard, the same as the race cutoff. The 50K is not on the list.

Can you have a pacer at Lake Sonoma?

No. Pacers are not allowed in any of the April races, and neither are trekking poles.

Is there cell service at Lake Sonoma?

Not much. The race calls cell service spotty at best, with none in many areas and none at Warm Springs. Download the course map in Goat Maps before you go: your phone's GPS still shows where you are without a signal.

Can you camp at the Lake Sonoma start?

Yes, on Friday and Saturday nights, next to the start and finish, with no reservation. Vehicles must fit in a standard parking space, and trailers are not allowed. Tents go in the marked area only.

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Updated . An unofficial guide, from the organizer's published information. Coordinates from the organizer's course and OpenStreetMap contributors. Photos from Unsplash. Organize a race? We help with course files.