Skinwalker

GPS finds you by timing how long a radio signal takes to arrive from a satellite. If that signal first bounces off a nearby cliff or mesa, it travels a longer path and shows up a little late, and the receiver counts that delay as extra distance. Think of shouting in a canyon: the echo reaches you after your real voice because it took the long way around. A bounced GPS signal fools the receiver the same way.

Could account for this reading (about 205 feet)

GPS combines signals from several satellites, but every satellite it can hear sits somewhere above you, never below. With nothing underneath to measure against, it pins down your side-to-side position far more confidently than your height, so a small timing error balloons into a large up-or-down error. Picture judging a friend's exact height while looking straight down from above: easy to see where they stand, hard to tell how tall they are. GPS has that same blind spot for altitude.

Could account for this reading (about 500 feet)

Roughly 50 to 1,000 km overhead lies the ionosphere, a layer of electrically charged particles stirred up by the Sun. GPS signals slow as they cross it, and slower means later, which the receiver reads as extra distance. The effect grows when the satellite sits low on the horizon, since the signal plows through more of the layer, and during solar storms. It works like sound dragging through fog instead of clear air: the signal gets held up, and the receiver never knows.

Can't account for this on its own (about 47 feet)

The troposphere is the weather layer, the moist, dense air close to the ground. Water vapor and air pressure slow the signal slightly, adding a small apparent distance. It is a gentler effect than the ionosphere, usually a few feet, and receivers already model most of it away. Compare it to a straw that looks bent where it enters a glass of water: the medium nudges the signal off its ideal timing, just by a little.

Can't account for this on its own (about 24 feet)

Einstein showed that gravity bends space and slows time, so a signal passing near a heavy mass arrives slightly late and nearby clocks tick slightly slow. This is real, and GPS already corrects for the everyday amount. But for gravity alone to throw the reading off this much, you would need a ridiculous amount of mass hidden underground. Imagine a bowling ball on a trampoline bending the path of a rolling marble: to bend a GPS signal by hundreds of feet, that bowling ball would have to weigh as much as hundreds of Earths, which plainly is not buried under a Utah ranch.

Can't account for this on its own (far less than an inch)

Heads up: this one is the project's own speculative idea, not established science and not a claim made by the show. Because GPS position is really a measurement of time, a distortion of time itself at the ranch could make the receiver report a position from a different instant than now, which might be one way to explain some of the strange results filmed on the show. And since Earth never stops moving, spinning on its axis, orbiting the Sun, and riding with the galaxy, a tiny slip in time becomes a real slip in position. For example, snap a photo a second late from a moving train and the whole scene shifts, because the train kept traveling during that second. The numbers below show how far Earth would travel, and so how large the time slip would be, for each of its motions.

Shows the time slip each motion would require