Start with the National Park Service app; it drift hunters has information on wheelchair accessibility at more than 400 sites. You may get an accessible map of the park's trails and additional information on their grade, quality, and stiffness on the park's website. You may also find out whether the park offers any loaner equipment to enhance your visit there. For use on the sand dunes at Great Sand Dunes National Park, for instance, the park provides wheelchairs with balloon tyres.