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. The section from Silverton to Ouray is frequently called the Million Dollar Highway. It is one of the roads on the Trails of the Ancients Byway, one of the designated New Mexico Scenic Byways.

U.S. 550 begins just north of Albuquerque at Bernalillo and passes through the towns of San Ysidro, Cuba, Bloomfield, and Aztec. Except for sections passing through the above listed towns, U.S. 550 in New Mexico has been widened to four lanes, offering a faster (70 mph) connection for Farmington, New Mexico and Durango, Colorado to Albuquerque and Santa Fe.

Most of U.S. 550 in Colorado is two-lane mountainous highway. It is one of only two north–south U.S. Highways in Colorado which runs west of the Continental Divide. (The other route is US 491.) The route travels north through the San Juan Mountains.

The Million Dollar Highway stretches for about 25 miles (40 km) in western Colorado and follows the route of U.S. 550 between Silverton and Ouray, Colorado. It is part of the San Juan Skyway Scenic Byway. Between Durango and Silverton the Skyway loosely parallels the Durango and Silverton Narrow Gauge Railroad.

Although the entire stretch has been called the Million Dollar Highway, it is actually just the twelve miles (19 km) south of Ouray through the Uncompahgre Gorge to the summit of Red Mountain Pass which gives the highway its name. 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. During this ascent, the remains of the Idarado Mine are visible. Travel north from Silverton to Ouray allows drivers to hug the inside of curves; travel south from Ouray to Silverton perches drivers on the vertiginous outside edge of the highway. Large RVs travel in both directions, which adds a degree of challenge to people in cars. The road is kept open year-round. Summer temperatures can range from highs between 70–90 °F (21–32 °C) at the ends of the highway to 50–70 °F (10–21 °C) in the mountain passes. The snow season starts in October, and snow will often close the road in winter. Chains may be required to drive.

North of Durango, the highway passes by Trimble Springs, hot springs that have been open for visitors since the late 19th century. The highway runs north along the Animas River, under the Hermosa Cliffs. It enters the San Juan National Forest and goes past Haviland Lake and Electra Lake. Drivers pass by Engineer Mountain and Twilight Peak before crossing Coal Bank Pass. Next is Molas Pass, which offers a panoramic view of Molas Lake, the Animas River Gorge, and Snowdon Peak. Northbound travelers then pass through the town of Silverton, elevation 9,320 feet (2841 m), surrounded by 13,000 foot (4000 m) peaks Sultan Mountain, Kendall Mountain, and Storm Peak.

The highway leaves Silverton and proceeds up Mineral Creek Valley before ascending to Red Mountain Pass. The ruins of the Longfellow Mine are visible along the way. 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.

This section of the route passes over three mountain passes:

• Coal Bank Pass, elevation 10,640 ft (3,240 m).
• Molas Pass, elevation 10,970 ft (3,340 m).
• Red Mountain Pass, elevation 11,018 ft (3,358 m).

The origin of the name Million Dollar Highway is disputed. 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.

There are seventy named avalanche paths that intersect Highway 550 in the 23 mi (37 km) between Ouray and Silverton, Colorado.

U.S. 550 ends at the corner of Townsend Avenue and San Juan Avenue in Montrose, Colorado at the junction of its parent route U.S. Highway 50.

The original portion of the Million Dollar Highway was a toll road built by Otto Mears in 1883 to connect Ouray and Ironton. Another toll road was built over Red Mountain Pass from Ironton to Silverton. 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. The remaining eight miles (13 km) were considered too difficult and steep for a railroad. At one point a cog railroad was proposed, but it never made it beyond the planning stage.

In the early 1920s, the original toll road was rebuilt at considerable cost and became the present day US 550. The Million Dollar Highway was completed in 1924. Today the entire route is part of the San Juan Skyway Scenic Byway.

US 550 was part of the original 1926 federal highway system. The original highway extended 110 miles (177 km) from Montrose, Colorado at U.S. Highway 50 to U.S. Highway 450 (now U.S. Highway 160) at Durango, Colorado. In 1934, Highway 550 was extended through Farmington to Shiprock, New Mexico. In 1989, the western end of US 550 was replaced with US 64 between Farmington and Shiprock. In 2000, US 550 was extended further south from Aztec to Bernalillo to replace the newly widened NM 44 and NM 544, at which time all of US 550 in New Mexico was four lanes.

In 2009 US 50 was re-routed onto the San Juan Avenue bypass to avoid downtown Montrose. As a result, U.S. 550 was extended approximately one mile northwest to intersect with the new U.S. 50 alignment.

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.

State	County	Location	mi	km	Destinations	Notes
New Mexico	Sandoval	Bernalillo	0.000	0.000	NM 165 east – Placitas	Continuation east beyond southern terminus
					I-25 / US 85 north (CanAm Highway) – Santa Fe, Las Vegas, Raton I-25 / US 85 south (CanAm Highway) – Albuquerque	Southern terminus; I-25 exit 242
					NM 313 north (Camino Del Pueblo) – Santa Ana Pueblo, Algodones, San Felipe Pueblo NM 313 south (Camino Del Pueblo) – Pueblo of Sandia Village, North Valley
			2.440	3.927	NM 528 south – Rio Rancho	Northern end of NM 528
		San Ysidro	23.225	37.377	NM 4 north – San Ysidro	Southern end of NM 4
		​	63.381	102.002	NM 197 south – Torreon	Northern end of NM 197
		Cuba	64.346	103.555	NM 126 east – Santa Fe National Forest	Western end of NM 126
		​	68.025	109.476	NM 96 north – La Jara	Southern end of NM 96
		​	85.485	137.575	NM 537 north	Southern end of NM 537
	Rio Arriba	No major junctions
	San Juan	​	123.470	198.706	NM 57 south	Northern end of NM 57
		Bloomfield	151.746	244.212	US 64 west – Farmington, Taos	Southern end of US 64 concurrency
			152.061	244.718	US 64 east – Navajo City	Northern end of US 64 concurrency
		Aztec	159.584	256.826	NM 516 west (Aztec Boulevard) – Farmington	Eastern end of NM 516
			161.470	259.861	NM 173 east – Navajo State Park	Western end of NM 173
			174.885 0.000	281.450 0.000	New Mexico–Colorado line
Colorado	La Plata	​	16.561	26.652	US 160 east – Pagosa Springs	Southern end of US 160 concurrency
		Durango	18.369	29.562	SH 3 north	Southern end of SH 3
			20.916	33.661	US 160 west – Cortez	Northern end of US 160 concurrency
	San Juan	No major junctions
	Ouray	Ridgway	103.702	166.892	SH 62 west – Placerville	Eastern end of SH 62
	Montrose	Montrose	129.306	208.098	SH 90 west (Main Street) – Naturita	Eastern end of SH 90
			130.219	209.567	US 50 east (North San Juan Avenue) – Sapinero, Gunnison North Grand Avenue west	Northern terminus
					US 50 west (North Townsend Avenue) – Olathe, Delta, Grand Junction	Continuation north beyond northern terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

• U.S. Route 50
• U.S. Route 150
• U.S. Route 250
• U.S. Route 350
• U.S. Route 450
• U.S. Route 650

• List of United States Numbered Highways
• Cascade Lodge

• Endpoints of U.S. Highway 550