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
Live conditions load in real-time — check back shortly.
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 predicts SR-203 closures and chain controls before the storm hits — plus calibrated snow forecasts, access timing, and smart alerts for 76 resorts.
Start 7-Day Free Trial — $500/yearCancel anytime · No commitment required