Interstate 70 in Utah

Interstate 70 (I-70) is a mainline route of the Interstate Highway System in the United States connecting Utah and Maryland. The Utah section runs east–west for approximately 232 miles (373 km) across the central part of the state. Richfield is the largest Utah city served by the freeway, which does not serve or connect any urban areas in the state. The freeway was built as part of a system of highways connecting Los Angeles and the Northeastern United States. I-70 was the second attempt to connect southern California to the east coast of the United States via central Utah, the first being a failed attempt to construct a transcontinental railroad. Parts of that effort were reused in the laying out of the route of I-70.

Unlike most Interstate Highways, much of I-70 in Utah was not constructed parallel to or on top of an existing U.S. Route. Portions of I-70 were constructed in areas where previously there were no paved roads. Because it was built over an entirely new route, I-70 has many features that are unique in the Interstate Highway System. For example, the 110 miles (180 km) stretch between Green River and Salina makes up the longest distance anywhere in the Interstate Highway System with no motorist services. This same piece is noted as the longest highway in the United States built over a completely new route since the Alaska Highway, and the longest section of Interstate Highway to open at a given time. The construction of the Utah portion of I-70 is listed as one of the engineering marvels of the Interstate Highway System.

The choice of the route had a significant impact on the character and culture of the Sevier Valley. It has also been a motivating factor for environmentalists to create a new national park along the path of the highway to protect scenic areas around the route. I-70 from Green River to Grand Junction, Colorado, is part of the Dinosaur Diamond Prehistoric Highway, making I-70 one of the few Interstate Highways to be named a National Scenic Byway. Attractions listed by the Federal Highway Administration (FHWA) for the Dinosaur Diamond Prehistoric Highway on or near I-70 include, Arches National Park, Canyonlands National Park, Cleveland-Lloyd Dinosaur Quarry, Goblin Valley State Park, Ruby Canyon, and Westwater Canyon. The designation also lists several side roads branching from I-70 that lead to dinosaur bones, footprints, and native petroglyphs.

I-70 begins at a trumpet interchange with I-15, near Cove Fort. It then proceeds east over the Pahvant Range, cresting at Clear Creek Summit with an elevation of 7,180 feet (2,190 m). The eastern descent from the Pahvant Range features bridges high above Clear Creek and its side canyons. The longest of these bridges is the Fish Creek bridge at 1,180 feet (360 m) long. The descent into Clear Creek features a brake check area and runaway truck ramp to aid truckers down the steep slope. The freeway then skirts the edge of Fremont Indian State Park and Museum before entering Sevier Valley.

I-70 serves as the main thoroughfare of the valley, the only area traversed by the highway in Utah with more than a few hundred residents. Richfield is the largest city along I-70 in the state. The highway enters the valley just north of Big Rock Candy Mountain, a mountain named for a song attributed to Harry McClintock. The highway proceeds northeast along the western edge of the valley, passing to the west of the communities of the valley, including Joseph, Monroe, Elsinore, and Richfield. As I-70 approaches Salina, it cuts across the valley passing to the south of the town. The highway avoids the downtown areas of all of these cities. The portion between Richfield and Salina is the busiest, with an annual average daily traffic (AADT) of 11,535 vehicles in 2006. In the Sevier Valley, I-70 was built parallel to U.S. Route 89; both highways now run concurrently between exit 23 (US-89 south to Marysvale and Panguitch) and exit 56 in Salina.

At Salina, US-50 joins I-70, and the two highways run concurrent for the rest of the way through Utah. After leaving exit 56 in Salina, I-70 departs on a 104-mile (167 km) course to the first Green River offramp, exit 160. Though there are a number of exits in between the two cities, it is the longest distance in the Interstate Highway System with no motorist services directly along the highway. The route to Green River crosses two major geographic obstacles: the Wasatch Plateau and the San Rafael Swell.

I-70 initially begins an ascent up the Wasatch Plateau via Salina Canyon. At lower elevations, this canyon separates the Wasatch Plateau to the north with the Sevier Plateau to the south. After climbing to a fork in the canyon, the highway turns south and crests the Wasatch Plateau at Emigrant Pass. This pass is the highest point of any of Utah's Interstate Highways, although the elevation differs from source to source. Newer Utah Department of Transportation (UDOT) maps list the elevation of 7,886 feet (2,404 m), while older maps give the figure 7,923 feet (2,415 m). This portion of I-70 is on protected lands as part of Fishlake National Forest. The highway exits the Wasatch Plateau at Fremont Junction, where I-70 meets Utah State Route 10 (SR-10).

Between Fremont Junction and the junction of SR-24 near Green River, I-70 crosses a geologic feature called the San Rafael Swell. The construction of the highway through the swell is listed as one of the engineering marvels of the Interstate Highway System, with one engineer claiming this section as "one of the most significant highway construction feats of its time". The construction of I-70 through the swell required boring through many solid rock canyons, cliffs, and mountains. The swell is noted for its sheer canyons and rock formations and is home to a large amount of exposed dinosaur remains. This includes the largest known collection of Jurassic-period dinosaur remains at the Cleveland-Lloyd Dinosaur Quarry at the north end of the swell.