Stone Mountain (Pennsylvania)
Encyclopedia
Stone Mountain is a stratigraphic
ridge
in central Pennsylvania
, United States
, trending northwest of the Jacks Mountain
ridge and Jacks Mountain Anticline
. The ridge line separates Kishacoquillas Valley
from the Seven Mountains area. Stone Mountain lies in, and the ridge line forms part of the border between, Mifflin
and Huntingdon
counties.
Pennsylvania Route 305
crosses the ridge and follows a valley along a fault line at 40°37′46"N 77°45′31"W near Greenwood Furnace State Park
. Allensville Road also crosses the ridge crest north of Allensville, and Barrville Road passes through a wind gap
west of Barrville. There are no water gap
s carrying rivers through the ridge. The Saddler Creek passes the southern foot of the ridge near the town of Mill Creek
.
Juniata Formation
on the southeast slope, and the younger more erosion resistant Silurian
Tuscarora Formation
geologic layer forming the steeper northwest slope and the crest. The Bald Eagle Formation crops out on the Kishacoquillas Valley-facing slopes of Stone Mountain, forming a steep topographic bench below the Juniata Formation. Below the Bald Eagle Formation, the uppermost sandstone layer of the underlying Reedsville Formation
contain brachiopods and other marine fossils. Across the Kishacoquillas Valley, on the opposite side of the Jacks Mountain anticline, the same rock layers are repeated in reverse order on Jacks Mountain
.
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
ridge
Ridge
A ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. There are several main types of ridges:...
in 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...
, trending northwest of the Jacks Mountain
Jacks Mountain
Jacks Mountain is a stratigraphic ridge in central Pennsylvania, United States, trending southeast of the Stone Mountain ridge and Jacks Mountain Anticline. The ridge line separates Kishacoquillas Valley from the Ferguson and Dry Valleys...
ridge and Jacks Mountain 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...
. The ridge line separates Kishacoquillas Valley
Kishacoquillas Valley
The Kishacoquillas Valley, known locally as both Kish Valley and Big Valley, is an enclosed anticlinal valley in the Ridge-and-valley Appalachians of Central Pennsylvania, lying between Stone Mountain ridge to the north and Jacks Mountain ridge to the south. The valley is located in Mifflin County...
from the Seven Mountains area. Stone Mountain lies in, and the ridge line forms part of the border between, Mifflin
Mifflin County, Pennsylvania
Mifflin County is a county located in the U.S. state of Pennsylvania. As of 2010, the population was 46,682. Its county seat is Lewistown. It is named after Thomas Mifflin, the first Governor of Pennsylvania.-Geography:...
and Huntingdon
Huntingdon County, Pennsylvania
Huntingdon County is a county located in the U.S. state of Pennsylvania. In 2010, its population was 45,913.Huntingdon County was created on September 20, 1787, from part of Bedford County. Its county seat is Huntingdon.-Geography:According to the U.S...
counties.
Pennsylvania Route 305
Pennsylvania Route 305
Pennsylvania Route 305 is an long state highway located in Huntingdon and Mifflin counties in Pennsylvania. The western terminus is at US 22 in Alexandria. The eastern terminus is at PA 655 in Belleville...
crosses the ridge and follows a valley along a fault line at 40°37′46"N 77°45′31"W near Greenwood Furnace State Park
Greenwood Furnace State Park
Greenwood Furnace State Park is a Pennsylvania state park in Jackson Township, Huntingdon County, Pennsylvania in the United States. The park is near the historic iron making center of Greenwood Furnace. The park includes the ghost town of Greenwood that grew up around the ironworks, old roads and...
. Allensville Road also crosses the ridge crest north of Allensville, and Barrville Road passes through a wind gap
Wind gap
A wind gap is a valley through which a waterway once flowed, but is now dry as a result of stream capture. A water gap is a similar feature, but one in which a waterway still flows...
west of Barrville. There are no water gap
Water gap
A water gap is an opening or notch which flowing water has carved through a mountain range. Water gaps often offer a practical route for road and rail transport to cross mountain ridges.- Geology :...
s carrying rivers through the ridge. The Saddler Creek passes the southern foot of the ridge near the town of Mill Creek
Mill Creek, Pennsylvania
Mill Creek is a borough in Huntingdon County, Pennsylvania, United States. The population was 351 at the 2000 census.-Geography:Mill Creek is located at ....
.
Geology
Just below the ridge crest lies the contact between the older OrdovicianOrdovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
Juniata Formation
Juniata Formation
The Ordovician Juniata Formation is a mapped bedrock unit in Pennsylvania and Maryland. It is a relative slope-former occurring between the two prominent ridge-forming sandstone units: the Tuscarora Formation and the Bald Eagle Formation in the Appalachian Mountains.-Description:The Juniata is...
on the southeast slope, and the younger more erosion resistant Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
Tuscarora Formation
Tuscarora Formation
The Silurian Tuscarora Formation — also known as Tuscarora Sandstone or Tuscarora Quartzite — is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:...
geologic layer forming the steeper northwest slope and the crest. The Bald Eagle Formation crops out on the Kishacoquillas Valley-facing slopes of Stone Mountain, forming a steep topographic bench below the Juniata Formation. Below the Bald Eagle Formation, the uppermost sandstone layer of the underlying Reedsville Formation
Reedsville Formation
The Ordovician Reedsville Formation is a mapped surficial bedrock unit in Pennsylvania, Maryland, Virginia, West Virginia, and Tennessee, that extends into the subsurface of Ohio. This rock is a slope-former adjacent to the prominent ridge-forming Bald Eagle sandstone unit in the Appalachian...
contain brachiopods and other marine fossils. Across the Kishacoquillas Valley, on the opposite side of the Jacks Mountain anticline, the same rock layers are repeated in reverse order on Jacks Mountain
Jacks Mountain
Jacks Mountain is a stratigraphic ridge in central Pennsylvania, United States, trending southeast of the Stone Mountain ridge and Jacks Mountain Anticline. The ridge line separates Kishacoquillas Valley from the Ferguson and Dry Valleys...
.