Coloradans are thinking about Christmas, not Memorial Day.

But if they’re wanting to camp that holiday weekend in the summer, they might want to start planning now.

Some of the state’s most popular campgrounds take reservations six months in advance. That includes campgrounds at Rocky Mountain National Park.

At the start of this month, a glance at Recreation.gov showed Memorial Day weekend spots starting to fill at the park’s largest campground, Moraine Park, as well as at Glacier Basin and Aspenglen campgrounds. Plenty of sites appeared to be available at the Timber Creek Campground on the national park’s western, Grand Lake side. At that campground and the others, some sites are set aside for booking 14 days in advance.

Meanwhile, Rocky Mountain National Park’s smaller Longs Peak Campground opens reservations at the start of January. That’s also the case at Piñon Flats Campground at Great Sand Dunes National Park and Preserve — what camping app The Dyrt has ranked as Colorado’s “hardest-to-book” campground.

That ranking also listed South Rim Campground at Black Canyon of the Gunnison National Park. At last check, Recreation.gov reservations had yet to be posted for the campground that was reportedly heavily damaged by this summer’s wildfire.

Along with national parks, Colorado’s national forests and state parks take reservations six months in advance.

Memorial Day weekend reservations are open for some of the most popular campgrounds in White River and San Juan national forests, as well as those closer to Front Range populations: Arapaho and Roosevelt and Pike and San Isabel national forests.

At the start of this month, sites for the holiday weekend appeared to be filling up at Chatfield and Mueller state parks, among parks close to Front Range populations.