A close-up view of Santiago Peak from the south, 50 miles down Hwy 385 from Hwy 90. The northeast wing of the intrusion can be seen from this angle, about 6,250 feet at the peak, 270 feet lower than the main body. The shapes of the two summits suggest that they are part of a plug, not an eroded sill. The flat top seen in the previous photo would therefore be the result of the uprising intrusion coming in contact with a resistant rock layer, perhaps a thick lava bed.
It is hard to believe that there were lava beds at this altitude when there are no traces of volcanic rocks of the main volcanic phase east of this point, but Elephant Mountain, 12 miles to the north is definitely a sill, the top of which is at 6,230 feet, so there has been a great amount of volcanic material removed in the last 30 million years.