Horizon Forbidden West is set in the Southwestern United States, specifically the states of Utah, Nevada, and California. Utah is claimed by the Carja and the Oseram, Nevada is predominantly controlled by the Tenakth, and the Quen have settled on small segments of California.
While the world of Horizon Forbidden West is inspired by the Western United States, it is not a 1:1 replica. Several artistic liberties are taken regarding the relative distance between real locations and their position relative to the prime directions, or by bringing two faraway locations extremely close together and leaving out vast swaths of territory in between. While some locations are directly based on their real-life counterparts, some only take visual inspirations, and other locations don't exist in the real world to begin with. For these reasons, it is impossible for the game map to be accurately laid over a real map of the Western United States.
Zion National Park and Beaver Dam Wash are now right next to each other, removing Red Cliffs National Conservation Area from the map.
Lake Mead is now right next to Beaver Dam Wash, removing Bunkerville from the map.
The Zion Human History Museum is now in Beaver Dam Wash, instead of Zion National Park.
In real life, the Very Large Array is in New Mexico, whereas here it appears to be somewhere between Utah and Nevada.
However, giving that the corresponding vista point refers to it as the "Western Grand Array", it's possible the Arrays we see in the game are a secondary location that doesn't exist in real life.
The Yucca Mountain Nuclear Waste Repository is not in the Desert National Wildlife Refuge.
In real life, Death Valley is to the west of Las Vegas, whereas in-game it's to the north.
The Crescent Dunes Solar Energy Project is now presented as if it's in Death Valley, whereas in real life it's 141 miles away in Tonopah.
However, giving that the corresponding vista point refers to it as the "Southwestern Solar", it's possible that it's a secondary location that doesn't exist in real life.
In real life, the section where the Los Angeles Aqueduct meets Interstate 5 is to the far southeast of the Big Sur and to the south of Sequoia National Forest, yet in-game it's just to the east in Sequoia National Forest.
Inyo National Forest has been removed from the map.
In real life, Crowley Lake is to the east of Mammoth Lakes, whereas in-game it's to the south.
Yosemite Valley meets the sea at its western end, even though in real life it is 150 miles away from the Pacific Ocean.
In-game holograms of Earth show the entire Central Valley submerged beneath the sea, which could explain Yosemite's proximity to the coast. However, if all icecaps were to melt, it would cause sea levels to rise by about 70 meters, and some parts of the Central Valley are well over 90 meters above sea level while other parts are well over 600 meters above sea level. The floor of Yosemite Valley itself is 4000 ft (1219 meters) above sea level, so seawater penetrating that far is simply not plausible.
Most of the Central Valley, including Stockton, Modesto and Fresno, has been removed from the map.
In real life, Oakland is to the far north of Bakersfield, yet in-game it's right next to the Fox Theater.
Bakersfield is also to the southeast of the Big Sur, yet it's to the northeast in-game.
There is a Fox Theatre in Oakland, which more closely matches the location of the Relic Ruin, so it's possible that the developers got the two mixed up.
In real life, San Francisco is to the far north northwest of the Big Sur, whereas in-game it's to the northwest.
San Francisco has been significantly compacted in the game, meaning various landmarks are a lot closer than they are in real life.
