The Nittany Arch or Nittany anticline is an anticline

Anticline

In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...

 geologic formation

Geologic formation

A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...

 in the western part of the Ridge-and-Valley

Ridge-and-valley Appalachians

The Ridge-and-Valley Appalachians, also called the Ridge and Valley Province or the Valley and Ridge Appalachians, are a physiographic province of the larger Appalachian division and are also a belt within the Appalachian Mountains extending from southeastern New York through northwestern New...

 physiographic province

Physiographic province

A physiographic province is a geographic region with a specific geomorphology and often specific subsurface rock type or structural elements.A continent may be subdivided into various physiographic provinces, each having a specific character, relief, and environment which contributes to its...

 of the Appalachian Mountains

Appalachian Mountains

The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...

 of Central Pennsylvania

Pennsylvania

The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The Nitany Arch is more than 100 miles (160 kilometers) long, stretching from Muncy

Muncy, Pennsylvania

For other places named 'Muncy', please see Muncy .Muncy is a borough in Lycoming County, Pennsylvania, in the United States. The name Muncy comes from the Munsee Indians who once lived in the area. The population was 2,663 at the 2000 census. It is part of the Williamsport, Pennsylvania...

 to Hollidaysburg

Hollidaysburg, Pennsylvania

Hollidaysburg is a borough in Blair County, Pennsylvania, on the Juniata River, south of Altoona. It is the county seat of Blair County. It is part of the Altoona, Pennsylvania, Metropolitan Statistical Area and is one of the communities that comprises the Altoona Urban Area...

, with a maximum width of approximately 9 miles (15 kilometers).

During the Appalachian orogeny, the sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 layers in this area folded up, forming the Nittany Arch. The arch was an ancient Himalayan scale mountain that towered above what is now Nittany Valley

Nittany Valley

The Nittany Valley is an eroded anticlinal valley in the central portion of Centre County, Pennsylvania in the United States. It is separated from the Bald Eagle Valley by Bald Eagle Mountain and from Penns Valley by Mount Nittany. The valley is closed to the north by a high plateau that joins...

. It has since eroded leaving its many rock layers exposed with the youngest rock layers at the foot of the Allegheny Front

Allegheny Front

The Allegheny Front is the major southeast- or east-facing escarpment in the Allegheny Mountains in southern Pennsylvania, western Maryland, and eastern West Virginia, USA. The Allegheny Front delineates the Ridge-and-Valley Appalachians to its east from the Appalachian Plateau to its west...

. The more durable rock layers have left the surrounding sandstone ridges above the limestone valleys.