You can make fast landscape studies with markers. Instead of dealing with all the colors, try a small set of gray markers (here I use Copic toner gray markers). Be careful, these markers will bleed through thin paper to leave marks on the next pages in a sketchbook. Try heavy paper or placing a blotter sheet below the one you are working on.
Click on one of the steps below to see the full size sketch and step-by-step instructions.
Lay in the light values with a pale gray marker. Leave a rim of light along the hilltops. Carve the shapes of the clouds with the same value.
With a marker of a slightly darker value, fill in the shapes of the distant woodlands, foreground shadows, and the tops of the ridges in the middle ground. Note that there is no edge on the background hills.
Block in the shapes of the foreground trees and woodland. Keep the outline of the clumps of vegetation irregular.
With a final, darkest marker, fill in the core shadows of the foreground trees. Leave a rim of the lighter value at the top of the trees to suggest backlighting.