Brush Mountain

Infobox Mountain
Name = Brush Mountain
Photo = BrushMtn.jpg
Caption =The higher soutwest section of Brush Mountain looking southwest toward Altoona. Interstate 99 is lower right. The Allegheny Front is center right, with Blue Knob in the center.
Elevation = 2,557 feet (779.4 m)
Coordinates = coord|40|29|15.68390|N|78|21|07.78634|W|type:mountain_region:US
Location = Pennsylvania, USA
Range = Appalachian Mountains
Prominence =
Topographic
USGS Millheim (PA) Quadrangle
First ascent = unknown
Easiest route =

Brush Mountain is a stratigraphic ridge in central Pennsylvania, United States, running east of the Allegheny Front and west of Tussey Mountain. It lies along the southeast side of Little Juniata River and both sides of the Sinking Run, and is the westernmost ridge in its section of the Ridge-and-valley Appalachians. The western ridge line separates the Logan Valley from the Sinking Valley.

Brush Mountain lies entirely in Blair County. It runs from the water gap formed with Bald Eagle Mountain by the Little Juniata River at Tyrone, south to the Sinking Valley anticline fold near Altoona then north to the Canoe Valley syncline fold, where the ridge becomes Canoe Mountain, a distance of approximately 30 miles (44 km).

No major roads or rivers cross the ridge or run through gaps. Kettle Reservoir collects surface runoff from a small area in the fold, and the dam was made by filling in a small ravine. Kettle Road, a secondary road, also runs through the ravine near the dam to the Sinking Valley. A major power transmission line crosses the ridge twice, midway between the folds.

The Brush Mountain Ridge is popular with soaring birds and glider pilots ridge soaring along its slopes. This ridge is part of a chain of ridges that stretch south to Tennessee. The fold at the south end of Brush Mountain forms a gap in the chain, with the continuation of the ridge line 10km south on Dunning Mountain.

Geology

Brush Mountain is in the western part of the Ridge and Valley province of the Appalachian Mountains. Bald Eagle Mountain, and neighboring Tussey Mountain ridge, are Paleozoic rock formations, consisting of older Ordovicial Bald Eagle Formation Sandstone and Juniata Formation Shale, and newer Silurian Tuscarora Formation Quartzite that were folded up during the Appalachian orogeny then eroded down to their present form.

The Tuscarora Quartzite is more erosion resistant than Bald Eagle Sandstone, and both are more durable than the Juniata Shale sandwiched in-between. Softer rock layers on either side of these eroded, leaving a double ridge line. On the north end of the mountain, the rock layers are tipped near vertical, and the mountain has the same double crested ridge shape as the Bald Eagle ridge extending to the north, with the crests near the center of the harder rock layers. A little further south, there are several fault lines running across the ridge, and the rock layers then slope down to the west. This leaves the Tuscarora formation more parallel to the steeper western slope, with the crest marking the dividing line between the layers. The tougher rock also protected the slope from erosion, leaving a higher southern ridge line.

The tilted aspect of the rock layers leaves the Juniata formation more perpendicular to the upper portion of the shallower opposite slope, below the steep crest. The Bald Eagle formation below holds back the eroding rock, creating a shelf above a steeper lower slope running down to the Sinking Valley. The drainage in the shelf area cut a series of small ravines, leaving terraces between them. The terraces wrap around the inside of the anticline fold around the Sinking Valley, and then around the outside of the reverse fold on Canoe Mountain.

"See also: Geology of Bald Eagle Mountain"