Rocky Mountain tree identification, from foothills to treeline

Foothills and mesas: piñon, juniper and cottonwood

Below the main forests, on dry mesas and the lower slopes, trees are small and spaced apart.

• Piñon pine (Pinus edulis): two stout, light green needles per bundle, 1 to 1 1/2 inches long; cones 1 to 2 inches; bark gray and smooth when young, red-brown and furrowed later. It grows 20 to 50 feet tall at 5,200 to 9,000 feet (Colorado State Forest Service).
• Rocky Mountain juniper (Juniperus scopulorum): small gray-green or silvery scale leaves instead of needles, berry-like cones about 1/4 inch across, and thin, fibrous gray-brown bark that shreds to show red-brown beneath. 20 to 50 feet tall at 5,000 to 9,000 feet. Junipers are often called cedars; the cedar page explains the difference, and the juniper page compares the western junipers.
• Plains cottonwood: on the eastern plains and along rivers at 3,500 to 6,500 feet, with glossy, yellow-green, toothed leaves 3 to 6 inches long and bark that becomes dark gray and deeply furrowed.
• Narrowleaf cottonwood: along mountain streams, with slender, lance-shaped leaves about 3 to 4 inches long on flattened stalks. The park's deciduous tree guide notes that young trees look like willows; cottonwood catkins hang limp, willow catkins stand upright.

Never eat a seed, berry or nut on the strength of a web page or an app; check with a local expert.

The montane zone: ponderosa pine, Douglas-fir and blue spruce

Rocky Mountain National Park places the montane zone at roughly 5,600 to 9,500 feet, where ponderosa pine and Douglas-fir dominate.

• Ponderosa pine (Pinus ponderosa): stiff, dark yellow-green needles 3 to 7 inches long, three per bundle; cones 3 to 4 inches; mature bark red-orange and split into large, flat, scaly plates. The park service notes that on warm days the bark smells like vanilla or butterscotch, so press your nose to a sunny trunk.
• Douglas-fir (Pseudotsuga menziesii): soft, flat, fragrant needles 3/4 to 1 inch long, attached singly; cones 1 1/3 to 3 inches with three-pronged papery bracts poking out between the scales. Despite the name it is neither a true fir nor a spruce. The Douglas-fir page covers the coastal variety too.
• Colorado blue spruce (Picea pungens): needles 1 to 1 1/4 inches, rigid and sharp, with new growth silver-blue; cones 2 to 4 inches. In the wild it grows in small groves along streams, but it is planted in yards across the region.

Lodgepole pine and quaking aspen: the middle heights

Both span a wide band of elevation, from the montane zone up into the subalpine.

• Lodgepole pine (Pinus contorta): two needles per bundle, 1 to 3 inches, often twisted and more yellow-green than other conifers; cones up to 2 inches; thin, light brown bark with many small scales. Trees are 20 to 80 feet tall.
• Quaking aspen (Populus tremuloides): smooth, greenish-white bark with black spots and lines, and nearly round, saw-toothed leaves that turn yellow, orange and red from early September into October. In Rocky Mountain National Park it grows from about 5,600 to 11,000 feet and reaches 30 to 65 feet (National Park Service). The poplar page separates aspen from cottonwoods.

The subalpine zone: spruce, fir and the five-needle pines

Just below treeline, between about 9,000 and 11,000 feet in the park, dense dark forests of spruce and fir take over.

• Engelmann spruce (Picea engelmannii): deep blue-green needles 5/8 to 1 inch, four-sided so they roll between finger and thumb, with a skunk-like smell when crushed. Papery cones 1 to 2 inches cluster in the top third of the tree. The Montana Field Guide calls it very common across the mountains of western and central Montana, often along streams.
• Subalpine fir (Abies lasiocarpa): flat, soft blue-green needles 1 to 1 1/2 inches that curve upward on the twig; cones 2 to 4 inches that stand upright, the only Rocky Mountain conifer to do so; young bark gray and smooth with resin blisters. Trees are 60 to 100 feet tall.
• Limber pine (Pinus flexilis): five needles per bundle (sometimes four), 1 to 3 inches long (the park service gives 1 to 2, the Colorado State Forest Service 2 to 3), usually on a small tree with a broad, flat-topped crown.
• Bristlecone pine (Pinus aristata): usually five needles per bundle, under 1 inch, dark with white lines; 15 to 30 feet tall at 9,200 to 11,800 feet in Colorado.

The northern Rockies: western larch

In western Montana and Idaho the mix changes. Western larch (Larix occidentalis) has needles 2 to 5 cm long in clusters of 15 to 30 on short spurs, cones 25 to 40 mm long, and thick, deeply furrowed bark with cinnamon-colored plates. The Montana Field Guide says large trees reach 60 m and can live more than 700 years. It is a larch like the tamarack of the north woods.

Using a photo on the trail

Conifer branches are often out of reach. Pick up a fallen cone and a twig, and photograph them together on your palm. Tree Identifier names a tree from one photo of a twig, cone, bark or leaf, and its follow-up chat can answer "is this Engelmann spruce or blue spruce?". It needs a data connection, which high trails may not have, so take the photos and identify them later from your library. It shows no confidence score, so check the result against the table above. The app's Collection includes ponderosa pine, Colorado blue spruce and Douglas-fir, and the Tree Map keeps the place of each find you locate.