The Spring Equinox marks the day the Sun crosses the celestial equator from South to North. This means more direct sunlight and warmer temperatures for those residing north of the equator.
This is an exciting time for the outdoor industry. As snow melts and lakes unfreeze, outfitters and adventurers across the country transition from snowsports to warm weather pursuits.
In the Outdoor Industry the Spring months of April and May are referred to as the "mud season". As the snow melts it leaves behind muddy hiking trails and forest roads for weeks before they eventually dry up making them easier to use and travel on. Many state and national campgrounds are still closed during the mud season, but if you are adventurous and resourceful enough to seek out dispersed and BLM campgrounds, this can be a rewarding time to go. Tourist travel is low until Summer kicks in meaning a better chance you will have the landscape to yourself.
Check out this great post by the Old Farmers Almanac for more details on the Spring Equinox: