Pinnacle Mountain is not a
volcano. Despite resembling a
cinder cone (a small conical volcano), Pinnacle Mountain is composed of
sedimentary rock, the
Jackfork Sandstone. Named after
Jackfork Mountain in
Oklahoma, the Jackfork Sandstone is an exceptionally hard
quartzitic sandstone;
weathered surfaces are usually
beige in color, while fresh surfaces tend to be much lighter. The Jackfork Sandstone can exhibit
conchoidal fracturing, a defining characteristic of
quartz, which, along with its great hardness, suggests the possibility of a
metasandstone. The
sediment that eventually formed the Jackfork Sandstone was deposited in the ocean prior to the
Ouachita Orogeny, the event that formed the
Ouachita Mountains. During the early
Pennsylvanian, slope collapse on the edge of the
continental shelf emptied vast quantities of
sand into a deep trough, which was slowly buried and transformed into sandstone. During the middle Pennsylvanian, the collision of two
continents,
Laurasia and
Llanoria, resulted in
uplift of the Ouachita Mountains, completing the assemblage of the
supercontinent Pangea. The Ouachita Mountains have been above
sea level undergoing
erosion since the late Pennsylvanian, approximately 300 million years ago. Pinnacle Mountain is a remnant of the rock deep within this ancient mountain range. ==Hiking==