Why it matters: The arrival of the copper-colored cuties offers another reason to check out the often-overlooked Rocky Mountain Arsenal ... enter and open daily from sunrise to 8pm.

Bison at Rocky Mountain Arsenal National Park (SkyFOX ... including the calves, for free from sunrise to sunset.

These include Acadia, Arches, Glacier, Haleakalā, Rocky Mountain, Shenandoah, and Zion National Parks. Reservations can often be made on Recreation.gov, and some parks offer day-before options.