The route's western terminus is at
Minaret Summit, on the border of
Mono County and
Madera County approximately 7 miles northeast of
Devils Postpile National Monument. It then heads east and intersects with Mammoth Scenic Loop Road, before entering the town of
Mammoth Lakes, where it is known as both "Minaret Road" and "Main Street". It continues east to its eastern terminus at
U.S. Route 395. West of SR 203's western terminus, the road continues locally as "Postpile Road" or "Minaret Summit Rd" for 8.5 miles passing
Devils Postpile National Monument and ending at Red's Meadow Resort and Pack Station. East of US-395, the road continues for 1.7 miles as "Old Hwy" connecting utility yards and rural residences to the route. Minaret Summit receives significant snowfall during the winter. The highway usually closes between Minaret Summit and the Main Lodge of
Mammoth Mountain Ski Area before
Thanksgiving and usually does not open much before
Memorial Day. There is no actual road closure gate here, as the highway is simply not plowed past the area west of the lodge where ski lifts cross over the road. ==Major intersections==