In general, pets are only permitted in National Parks along roadways, in developed areas and in campgrounds, and must be restrained on a leash no longer than 6 feet in length, caged or crated at all times. Pets are not permitted inside buildings, on most trails, on beaches, or in the back country.
In National Forests pets must be restrained or on a leash at all times while in developed recreation areas. Dogs are permitted on national forest trails, but are not permitted in swimming areas or sanitary facilities.
Always clean up after your pet and never leave your pet unattended.