The Chicago Tribune carried a great piece in December 2015 about the ability to choose national parks as a final resting place. Many parks allow the scattering of cremation remains, but each park’s rules are different. The National Park Service has a list of the offices that manage each park, and you can find out more about each park’s rules by contacting its office. (The Bureau of Land Management also has a list of frequently-asked questions about scattering ashes on its site, linked above.)
Talking to your family about your preferences regarding burial or cremation is important. If you choose cremation, it can also help to talk to family about what to do with your ashes afterwards.