The greatest concentration of backcountry airstrips in the Continental United States is found in the Northwest. Idaho has by far the largest number, mostly due to the diligence of Idaho pilots who have banded together to work with state and federal agencies and land owners to keep airstrips open on public and private lands. Unfortunately, most Northwest backcountry airstrips are inaccessible for at least half the year, due to a combination of high latitudes and mountain altitudes. But savvy backcountry pilots who enjoy winter flights know where the snow-free strips are—in Hells Canyon.
Source: aopaAll-winter backcountry access