The Medicine Bow Range, bordering the park's east side, resulted from localized crustal movements that uplifted the entire region during the Mesozoic era. Thrust faulting, where one crustal end is pushed over the other, impacted State Forest State Park. Since there were multiple faults, slices between faults were exposed, including the iconic Nokhu Crags. Originally shale, the Crags metamorphosed into hard hornfels due to magma eruptions from below.

Volcanic eruptions covered the region in lava flows, remnants of which are visible on Iron Mountain. Erosion revealed fault slices, exposing the near-vertical hornfels layers forming the Nokhu Crags. Glaciers shaped the landscape we see today, carving cirques where high mountain lakes have formed.

The East Sand Dunes Natural Area features the only undisturbed, cold-climate dune in Colorado, unique for its sedimentary structures. Unlike North Sand Dunes, East Sand Dunes is not open for OHV use, preserving its natural state. Geologically distinct from the Great Sand Dunes National Monument, North Park's dunes formed as winds carried sand from eroded peaks. When winds hit the Medicine Bow Mountains to the east, they slowed, depositing sand at North Park's edge, creating dunes. Both East and North sand dunes are part of a larger, mostly dormant dune system spanning approximately 25 square miles.

The park's climate mirrors high Rocky Mountain valleys, featuring abundant sunshine, low humidity, low precipitation and significant temperature variations. As elevation increases, temperatures drop and precipitation rises. Annual precipitation varies across the forest, exceeding 100 inches in some areas.