Ninety million year-old bedrock is exposed near the entrance to the park along Iowa Highway 12. The roadcut exposes lignite, shale, sandstone, and limestone. Fossils of marine organisms can be found in the Cretaceous bedrock.

Wildlife and Plants
Stone Park is recognized nationally as an "Urban Wildlife Sanctuary". Wild turkeys, white-tailed deer, coyotes, and red foxes can be found here. A variety of birds can be seen, including: turkey vultures, barred owls, rufous-sided towhees, and ovenbirds. Rare butterflies, such as the Pawnee skipper and Olympia white, are found on the prairie ridges.

Bur oak is the predominant tree species in the park. Late April and early May are the best times to view the woodland wildflowers. A wide array of prairie plants can be found on the steep, dry, slopes, including: yucca, penstemon, rough blazingstar, silky aster, and pasque flower. The Mt. Talbot State Preserve covers the northern most 90 acres of the park.