A mosaic of yellows, oranges, and reds has begun to light up the area’s mountainsides. For travelers along the San Juan Skyway and other mountain roads, it would be difficult not to notice the new striking colors.

Phil Kemp, timber-management assistant at the Dolores Ranger District of the San Juan National Forest, said that this year’s autumnal changes are likely to peak this coming weekend. Currently, the San Juan Mountain’s three main species of deciduous trees —aspen, cottonwood, and Gambel oak — are quickly turning colors.

Interspersed with those trees are large groves of green conifers. Englemann spruce, sub-alpine fir, blue spruce, and an occasional Douglas or white fir provide a deep-green background for the waves of changing leaves.

Aspen grow from shared root systems at moderate to high elevations, so different clumps, or clones, of aspen trees will change colors together. Cottonwoods grow in riparian areas along rivers and creeks, and Gambel oaks are found at lower to middle elevations.

Autumn colors exist in leaves year-round but are hidden by chlorophyll, which produces the dominant green color. Trees use chlorophyll to convert sunlight into food. Changes in daylight, and to a lesser extent, temperature, slow food production in fall. As chlorophyll decreases, so does the green color, allowing hidden pigments to show through.

Kemp said that the temperatures and climate leading up to the color change, called "photo-period," determines the intensity, length, and timing of the display. Leaves change color in response to the decreasing amount of daylight in autumn, but weather conditions, such as cooler temperatures, early frosts or drought, play a significant part.

Elevation, latitude and slope aspect also determine when trees turn color. Hence, colors turn first farther north and at higher elevations.

This year’s tinder-dry summer has not damaged the brilliance of the colorful fall, said Kemp. "A drought will generally cause a little bit earlier color change, and I think probably a little more intensive one — meaning the colors are more brilliant," he explained.

The Forest Service has suggested the following roads for aspen-viewing. For an autumnal walk, Kemp said to check out Hillside Drive in Dolores.

• West Dolores/Meadows (Forest Rd. 535)

• Meadows (Forest Rd. 535)

• Black Mesa (Forest Rd. 611)

• Taylor Mesa (Forest Rd. 545)

• Stoner Mesa (Forest Rd. 686)

• Haycamp Mesa (Forest Rd. 556)

• Echo Basin (Forest Rd. 566)

• West Mancos (Forest Rd. 561)

• Lime Creek Road (Forest Rd. 591)

• Junction Creek Rd. (Forest Rd. 171)

• Missionary Ridge Rd. (Forest Rd. 682)

• Bolam Pass (Forest Rd. 578B)

• La Plata Canyon (Forest Rd. 571)

• Upper Hermosa (Forest Rd. 578)

• Middle Mountain (Forest Rd. 724)

• Beaver Meadows (Forest Rd. 135)

• Transfer Park (Forest Rd. 243)

• Alpine Loop (State Hwy 110 and 149, county roads 2 and 30)

• Ophir Pass (Forest Rds. 679 and 630)

• South Mineral (Forest Rd. 585)

• Stoney Pass (Roads 589, 737, 520