In one scene we see Vargas (the "Diablo Giant") coming to life and rising from his grave. But this is after there had been a brutal killing and cattle mutilations.
At end of movie when Vargas breaks thru the handrail of the bridge, a few seconds later the hero is seen walking off the bridge and the handrail intact.
During the climax between Vargas and Ed at the mill, you can see it snowing (and a little snow on the ground) followed by no snow (falling or on the ground). This goes back and forth more then once.
Vargas flips the passenger seat forward to aide in removing Janet Cleveland from the Jeep and has to carry her in both of his arms. The next time the Jeep is shown, the passenger seat is back in its normal position.
The Professor states a number of times that Vargas and his Conquistadors died over 500 years ago, and that their disappearance was documented by the Spanish at the time. However, this would date their expedition to least 70 years before the first Spanish expeditions into California, which took place during the 1520s and 1530s, and even well before Columbus "discovered" the West Indies.
The Professor claims that Tannic Acid in oak leaves has helped Vargas's armor to survive in a better condition than that of his followers. Oak leaves actually contain Tannins, which wouldn't have that effect.
Most of the the Conquistador's iron helmets, breastplates and weapons are in a perfect condition, despite being buried in the ground for over 400 years.
When Ed and Sally are having a romantic chat in front of a lake, the fully visible ripples in the water are still, hence they're in front of a photo of a lake.
The metal detectors used by Ed and the Professor can be clearly seen to be made out of plywood in close up shots.
When Wayne Brooks is metal detecting and comes upon the helmet and other metal artifacts, the metal detector is making random Geiger counter-like clicking sounds instead of varying tones that a metal detector makes.
When the metal detector is being used, it making very narrow sweeps instead of wide sweeps what would have covered more ground in the same amount of time.
Vargas picks up a man to throw him and wires are clearly visible.
While running away from the giant, Janet stops behind a boulder and it wiggles a little bit when she touches it, revealing it to be a lightweight prop.
It is never explained who or what is responsible for all the killings and mutilations discussed in the first five minutes - all of which take place well before Vargas The Giant is resurrected.
Wayne Craig says they are going above the snow line after they have looked at the reassembled stone cross. He probably meant the treeline since there is no such thing as a snow line.