Keyhole State Park
Northeastern Wyoming’s largest reservoir spreads among ponderosa pine, blocky sandstone bays, ten campgrounds, and more than 150 million years of shoreline geology.
Artwork inspired by Hans Kleiber
Keyhole wraps around a 13,700-acre Belle Fourche River reservoir, and its ten campgrounds are not interchangeable. Coulter Bay and Cottonwood put sandstone and water close together; Tatanka provides developed hookup and cabin options; Rocky Point, Pronghorn, Pat’s Point, Homestead, Arch Rock, Beach Area, and Wind Creek each solve a different access problem. Select the named loop before reserving or navigating.
The shoreline is a readable cross-section of a vanished continent. River-laid Morrison and Lakota formations predate the Western Interior Seaway; blocky Fall River sandstone records its advance, while dark shale and younger limestone record deeper water and shell-forming organisms. Between the dam and inlet, the Pine Ridge Anticline and Black Hills Monocline tilt those once-horizontal layers, making a geology stop useful even without a boat.
Water is the practical center of the visit. Wind, reservoir level, dock status, cold water, harmful cyanobacterial blooms, and fire restrictions can change swimming, launching, or camping plans quickly. Treat the official status page—not an old camping memory—as the final authority before departure.
- Reservoir
- 13,700 acres; northeastern Wyoming’s largest
- Campgrounds
- 10 named loops; reservations May 15–September 15
- Rock record
- More than 150 million years
Quick guide
- Begin
- Compare all ten named loops; Tatanka, Coulter Bay, Cottonwood, and the quieter points offer materially different access and services.
- Do not miss
- Confirm the chosen ramp or dock, wind forecast, reservoir level, and HCB notice before swimming, paddling, or launching.
Quick guide
- Choose a campground
- Compare all ten named loops; Tatanka, Coulter Bay, Cottonwood, and the quieter points offer materially different access and services.
- Read the shoreline
- Use the WSGS guide at Coulter, Cottonwood, Mule Creek, Wind Creek, or Deep Creek bays to identify changing seaway deposits.
- Match the water
- Confirm the chosen ramp or dock, wind forecast, reservoir level, and HCB notice before swimming, paddling, or launching.
- Respect the fire ban
- Current Stage 2 restrictions prohibit campfires and open flames; verify what approved gas equipment remains permitted.
Good to know
Harmful-algal-bloom monitoring and fire restrictions can change quickly. Avoid green water, scum, or clumps, keep pets and livestock away, and check the live fire rule before packing fuel or planning to cook.
Notice these
- Tan Fall River sandstone breaking into angular shoreline blocks around Coulter and Cottonwood bays
- Dark Skull Creek Shale beside lighter Newcastle Sandstone at Mule Creek Bay
- The Pine Ridge Anticline and Black Hills Monocline bending layers between reservoir inlet and dam