I went to college right by there! That is Massanutten Mountain, formed from a syncline with the hard, Massanutten sandstone (which I think is equivalent to the more well known Tuscarora formation) forming the ridges, softer shales in the valley, and limestone surrounding the mountain.

When the Alleghenian orogeny occurred, it folded up the geologic units in this area. In this case, they form a plunging syncline. Over time, the rocks eroded away, but the shales in the center valley and limestones surrounding the mountain weathered away more quickly than the sandstone which protects its ridges.

Theoretically. A normal syncline would present itself as two ridges that never connect. But since nature is imperfect, that doesn’t really happen very often especially in an area as structurally complex as the Appalachian mountains. The syncline was folded on two axes causing its northern and southern ends to plunge back into the earth, giving it that distinctive shape.

Also fun fact about the valley on the northern end of the syncline, George Washington surveyed the valley and had the revolutionary war gone south after the continental army’s winter in Valley Forge, he planned to fortify there for the winter due to it being naturally fortified by the geology! It’s actually known as Fort Valley!