Seneca Rocks is a large crag and local landmark in Pendleton County in the Eastern Panhandle of West Virginia, USA. It is easily visible and accessible along West Virginia Route 28 in the Spruce Knob-Seneca Rocks National Recreation Area. One of the best-known scenic attractions in West Virginia, the sheer rock faces of Seneca Rocks are a popular challenge for rock climbers. Seneca Rocks is at the northern end of the River Knobs, which contain other similar "razorback" ridges or "fins" such as Judy Rocks and Nelson Rocks. They are a prominent and visually striking formation rising nearly 900 feet above the confluence of Seneca Creek with the North Fork South Branch Potomac River. They also overlook the community of Seneca Rocks, traditionally known as "Mouth of Seneca". The Rocks consist of a North and a South Peak, with a central notch between. (Formerly, a prominent pinnacle — "the Gendarme" — occupied the notch.) Seneca Rocks and nearby Champe Rocks are the most imposing examples in eastern West Virginia of several formations of the white/gray Tuscarora quartzite. The quartzite is approximately 250 feet thick here and is located primarily on exposed ridges as caprock or exposed crags. The rock is composed of fine grains of sand that were laid down approximately 440 million years ago in the Silurian Period, in an extensive sand shoal at the edge of the ancient Iapetus Ocean. Eons of geologic activity followed, as the ocean slowly closed and the underlying rock uplifted and folded. Millions of years of erosion stripped away the overlying rock and left remnants of the arching folds in outcrops such as Seneca Rocks.