US-395 / SR-203 Mammoth (SR-203) Road Conditions & Closures
SR-203 · CA · closures driven by road-surface conditions
High closure risk
US-395 / SR-203 Mammoth (SR-203) is the main mountain-access corridor for Mammoth Mountain. It's a high-closure corridor, and when it shuts down or restricts traffic, the cause is almost always road-surface conditions. Below: live Caltrans status, plus StormDrop's read on when SR-203 tends to close and how to time your drive around it.
Live SR-203 Status
US-395 / SR-203 (Mammoth)
UnknownNo chain controls reported — road access unconfirmed. No chain controls are in effect at this time.. Chain checkpoints do not establish whether the route is open. Check Caltrans QuickMap for closures and current requirements.
When does US-395 / SR-203 Mammoth close?
Closure risk
High
Typical window
Any time
Typical reopen
~3 hr
Closures here aren't limited to a fixed morning window — they can happen at any time of day during an active storm, usually reopening about roughly 3 hours after control work wraps up.
In StormDrop's closure model, risk starts building once a storm cycle pushes past about 18" of new snow and climbs steeply above roughly 36". Sustained wind above about 35 mph adds risk through blowing and drifting snow.
Traction-law restrictions tend to appear well before a full closure — often around 6" of fresh accumulation — so carrying chains or running AWD/4WD with snow tires is the safe default on a storm day.
These are StormDrop's closure-model tendencies and general corridor knowledge — not a published schedule or a guarantee. Caltrans makes the real-time call. Always confirm live SR-203 status before you go.
Beating the closure
Closures here aren't tied to a set time — build slack into your plan and watch live status all morning.
Carry chains or run AWD/4WD with dedicated snow tires whenever a storm is in the forecast — a traction law can go up before the road ever closes.
Check the live Caltrans status above before you leave, and again mid-drive — storm-day conditions on SR-203 can flip within minutes.
Have a backup resort or a later-start plan so a control-work delay doesn't cost you the day.
Frequently asked
Is US-395 / SR-203 Mammoth open right now?
StormDrop shows live Caltrans status for SR-203 in the status block at the top of this page. Conditions change quickly during storms — treat the live status, not this page's general guidance, as the source of truth before you leave the driveway.
When does US-395 / SR-203 Mammoth usually close?
US-395 / SR-203 Mammoth is a high-closure corridor whose closures are driven mainly by road-surface conditions. Closures here aren't limited to a fixed morning window — they can happen at any time of day during an active storm, usually reopening about roughly 3 hours after control work wraps up. In StormDrop's closure model, risk starts building once a storm cycle pushes past about 18" of new snow and climbs steeply above roughly 36". Sustained wind above about 35 mph adds risk through blowing and drifting snow.
Do I need chains on SR-203?
On an active storm day it's wise to be ready. SR-203 through US-395 / SR-203 Mammoth can go under a traction law that requires AWD/4WD with snow tires or chains. Carry a set and check the live Caltrans status above before departing.
Never get skunked by a closed road again
StormDrop tracks SR-203 closures and chain controls against the storm forecast, plus access timing, storm alerts, and local knowledge for 27 mountains.
Start 7-Day Free Trial - $500/yearCancel anytime · No commitment required