U.S. Route 550 (US 550) is a spur of U.S. Highway 50 that runs from Bernalillo, New Mexico to Montrose, Colorado in the western United States.

[4] U.S. 550 begins just north of Albuquerque at Bernalillo and passes through the towns of San Ysidro, Cuba, Bloomfield, and Aztec.

This stretch through the gorge is challenging and potentially hazardous to drive; it is characterized by steep cliffs, narrow lanes, and a lack of guardrails; the ascent of Red Mountain Pass is marked with a number of hairpin curves used to gain elevation, narrow lanes for traffic—many cut directly into the sides of mountains.

[7] The highway leaves Silverton and proceeds up Mineral Creek Valley before ascending to Red Mountain Pass.

The highway then goes through a series of steep grades and hairpin turns before reaching Lookout Point, which offers a view of the town of Ouray.

There are several legends, though, including that it cost a million dollars a mile to build in the 1920s, and that its fill dirt contains a million dollars in gold ore.[3] There are seventy named avalanche paths that intersect Highway 550 in the 23 mi (37 km) between Ouray and Silverton, Colorado.

The original portion of the Million Dollar Highway was a toll road built by Otto Mears in 1883 to connect Ouray and Ironton.

In the late 1880s Otto Mears turned to building railroads and built the Silverton Railroad north from Silverton over Red Mountain Pass to reach the lucrative mining districts around Red Mountain, terminating at Albany just eight miles (13 km) south of Ouray.

On July 17, 2024, the segment of US 550 leading into Durango from the south was realigned onto a four-lane divided highway tying into the Grandview Interchange.

This realignment bypasses a former steep, curvy alignment up Farmington Hill and includes a new roundabout.