[3][4] Its proximity to the Arkansas River and steep south slopes make Pinnacle Mountain a prominent landform observable from many areas in Pulaski County.

Despite resembling a cinder cone (a small conical volcano), Pinnacle Mountain is composed of sedimentary rock, the Jackfork Sandstone.

[6] The Jackfork Sandstone can exhibit conchoidal fracturing, a defining characteristic of quartz, which, along with its great hardness, suggests the possibility of a metasandstone.

[7] 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.