The Huntley Mountain Formation is a late Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 and early Mississippian mapped bedrock unit in 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...

, in the United States

United States

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

.

Description

The formation is composed of relatively soft grayish-red shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

 and olive-gray sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

. It is located in north central Pennsylvania.

Haystacks

The Haystacks are enigmatic mounds of sandstone that outcrop in Loyalsock Creek south of Dushore

Dushore, Pennsylvania

Dushore is a borough in Sullivan County, Pennsylvania, in the United States. The population was 608 at the 2010 census. Dushore is home to Sullivan County's only traffic light.-Geography:Dushore is located at ....

 in Sullivan County

Sullivan County, Pennsylvania

Sullivan County is a county located in the U.S. state of Pennsylvania. As of 2010, the population is 6,428. Sullivan County was created on March 15, 1847, from part of Lycoming County and named for Charles Sullivan, leader of the Pennsylvania Senate...

. They are a single bed

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 of quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 with an undulating upper surface with up to one meter relief. The origin of the mounds is debatable.

Notable Exposures

• The type section of the formation is at Huntley Mountain in Lycoming County, Pennsylvania
  Lycoming County, Pennsylvania
  -Appalachian Mountains and Allegheny Plateau:Lycoming County is divided between the Appalachian Mountains in the south, the dissected Allegheny Plateau in the north and east, and the valley of the West Branch Susquehanna River between these.-West Branch Susquehanna River:The West Branch of the...
  
  , on the mountainside just north of the village of Waterville.
• Base of the Loyalsock Creek
  Loyalsock Creek
  Loyalsock Creek is a tributary of the West Branch Susquehanna River located chiefly in Sullivan and Lycoming counties in Pennsylvania in the United States...
  
   gorge in Worlds End State Park
  Worlds End State Park
  Worlds End State Park is a Pennsylvania state park in Sullivan County, Pennsylvania, in the United States. The park, nearly surrounded by Loyalsock State Forest, is in the Loyalsock Creek valley on Pennsylvania Route 154, in Forks and Shrewsbury Townships just east of the borough of Forksville....
  
  
• Haystacks beds, also in Loyalsock Creek

Stratigraphy

Geologist William E. Edmunds argues that the Huntley Mountain Formation is laterally equivalent to the Rockwell Formation

Rockwell Formation

The Rockwell Formation is a late Devonian and early Mississippian mapped bedrock unit in West Virginia, Maryland, and Pennsylvania, in the United States.-Description:...

 (originally described in West Virginia

West Virginia

West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...

) and the Spechty Kopf Formation. He proposes that the Pocono Formation

Pocono Formation

The Mississippian Pocono Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia, USA. It is also known as the Pocono Group in Maryland and West Virginia,...

 be reinstated as "the dominantly non-red, non-marine clastic sequence between the Catskill and Mauch Chunk Formation

Mauch Chunk Formation

The Mississippian Mauch Chunk Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia. It is named for the borough of Mauch Chunk, now known as Jim Thorpe, Pennsylvania.-Description:...

s", with the Huntley Mountain, Beckville, Burgoon, Rockwell, Mt. Carbon, and Spechty Kopf Formations demoted to the status of members of the Pocono Formation. Other workers support this interpretation.