Sean O’Brien 50 Miler (Calabasas): AC100 Qualifier Guide
A strong “systems test” 50 for LA runners. The terrain rewards runners who can keep effort even, manage small climbs, and fuel without drama.
Calabasas / Santa Monica Mountains
SoCal qualifier
Pacing discipline
Internal link: best 50-mile races to qualify for the AC100
Why this race is a smart AC100 qualifier
- Close to Los Angeles, so you can stay calm and arrive rested.
- Rolling climbs force you to control effort repeatedly.
- Great environment to practice a simple, repeatable fueling plan.
Course feel
This is not a “one big climb” mountain ultra. It’s repeated work. The difficulty is how small decisions add up: micro-surges, skipped calories, sloppy descents.
What to practice here for AC100
Pacing
- Keep early climbs easy.
- Run the flats at a sustainable cadence.
- Don’t chase people who are burning matches.
Fueling
- Set a timer for calories.
- Alternate sweet/salty to avoid gut shutdown.
- Drink to conditions; don’t under-salt if it’s warm.
LA logistics
- From SGV, plan for freeway time. Arriving stressed is free fatigue.
- Bring layers for early chill + later warmth. SoCal can swing.
Common mistakes
- Racing the first half like a marathon.
- Skipping calories because it “feels easy.”
- Letting small descents trash your quads.
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