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.
The distance between Zion National Park and Lake Mead is at least twice the distance in real life.
In real life, the Very Large Array is in New Mexico, whereas here it appears to be somewhere between Utah and Nevada.
The Memorial Grove is based on the Mojave National Preserve. However, there is no battlefield in it, nor is there a museum dedicated to said battlefield.
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 (such as Fresno) are well over 90 meters above sea level, and other parts (such as the Sierra Buttes) 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.