State

Old Oak Trail

North Dakota

Backcountry Trail

U.S. Corps of Engineers

Old Post Road Mountain Bike Trail

Arkansas

Backcountry Trail

City, Town, or County

Olentangy-Scioto Trail

Ohio

Rail Trail

City, Town, or County

Orange Heritage Trail

New York

Rail Trail

Bureau of Land Management

Oregon High Desert Trail

Oregon

Backcountry Trail

Bureau of Land Management

Organ Mountain Trails - Baylor Pass Trail

New Mexico

Backcountry Trail

Bureau of Land Management

Organ Mountain Trails - Pine Tree Trail

New Mexico

Backcountry Trail

National Park Service

Otis Pike Wilderness Nature Trail (Burma Trace)

New York

Backcountry Trail

U.S. Fish and Wildlife Service

Ottawa Wildlife Interpretive Trail

Ohio

U.S. Corps of Engineers

Ouachita Geo-Float Trail

Arkansas

Water Trail (other)

USDA Forest Service

Ouachita Trail

Arkansas, Oklahoma

Backcountry Trail, Urban Trail

U.S. Corps of Engineers

Outlet Campground Trail System

Kansas

Backcountry Trail, Urban Trail

U.S. Corps of Engineers

Overmountain Victory Trail

North Carolina

Backcountry Trail

Nonprofit

Oxley Nature Center Trails System

Oklahoma

Backcountry Trail

USDA Forest Service

Ozark Highlands Trail

Arkansas

Backcountry Trail

USDA Forest Service

Ozark Trail

Missouri

Backcountry Trail

National Park Service

Pacific Northwest Trail - Glacier National Park Segment

Montana

Backcountry Trail

National Park Service

Pacific Northwest Trail - North Cascades National Park/Ross Lake NRA Segment

Washington

Backcountry Trail

National Park Service

Pacific Northwest Trail - Olympic National Park Segment

Washington

Backcountry Trail

Commission

Paint Creek Trail

Michigan

Backcountry Trail, Frontcountry Trail, Rail Trail