The Back Road to Sun Valley Most People Are Too Nervous to Drive
Ask someone in Ketchum how to get to Mackay and they’ll route you the long way — south down the highway, east across the desert, and back up the valley. Two and a half hours. Ask someone in Mackay and they’ll point at the mountains and say “Trail Creek.”
Trail Creek Road goes straight over the top. It’s shorter, it’s emptier, and it’s the most beautiful drive within a day of either town. It’s also dirt for most of its length, it climbs to a 7,900-foot summit, and it closes with the first big snow every fall and doesn’t open again until sometime in May. Which is exactly why so many visitors look at it on the map, get nervous, and take the highway.
You should take Trail Creek.
The drive
From our side, you head north out of Mackay on US 93, up the valley with the Lost River Range on your right — Mount Borah, the highest point in Idaho, growing up ahead and to your right. At the tiny townsite of Chilly you turn west onto Trail Creek Road, and the pavement runs out.
For the next hour or so you’re on good graded dirt, climbing gently up the valley of the Big Lost River’s headwaters. This is the part people don’t expect: it’s not a white-knuckle mountain road, it’s a wide, open, high valley with hayfields giving way to sage, then sage to aspen and fir. Side roads peel off up every canyon — Wildhorse, the North Fork, Copper Basin — each one with its own creek and trailheads and a campground or two at the end. There are six developed campgrounds along the route, none with hookups or hosts, all of them the kind of place where you’ll hear the creek all night and nothing else.
This is also moose country. The willow bottoms along the creeks are exactly where they like to stand, so slow down and look, especially in the mornings.
Then the road turns up into the trees, switchbacks a couple of times, and tops out at Trail Creek Summit. Get out here. Look back east. The whole Lost River Range is lined up along the horizon, and if you time it for late afternoon, the light comes in sideways across all of it.
The part that makes people nervous
The west side of the pass — the Sun Valley side — is the steep side. The road drops down Trail Creek Canyon in a series of tight, narrow, shelf-road switchbacks with a long way down on the outside. This is the stretch that earns Trail Creek its reputation, and it’s why trailers aren’t allowed on the road.
Here’s the honest version: in dry summer conditions, in a regular car, driven at a sensible speed, it’s fine. Plenty of people do it every summer in minivans. It’s exposed, and it’s not for anyone who hates heights, but it’s a couple of miles, it’s well-graded, and then you’re on pavement rolling into Sun Valley past the Hemingway memorial and the ski hill.
Where it stops being fine is in the rain, in early spring before it’s dried out, or after dark. Don’t do it then. Take the highway.
Practical notes
Allow close to two hours from Mackay to Ketchum without stops, and you will stop. There’s no cell service for most of the route, so download your map first. Watch the road status before you go — it closes for the season around mid-November and opens again when the snow lets it, usually May, sometimes June in a big year. Any car with reasonable clearance is fine in summer; high clearance is nice on the side roads but not needed on the main route. Bring water, a full tank, and something warm; the summit is cold even in July.
And do it in both directions if you can. The road over from Sun Valley delivers you into the Lost River Valley with Borah filling the view, which is a much better way to arrive than the highway. The whole valley’s lodging is waiting at the bottom of the hill.