Douglas maple, Acer glabrum var. douglasii, is not exactly a common tree. I see them here and there at best.
I've seen them both west and east of the Cascades and at various elevations from sea-level to almost 4,000'/1,200m.
But I've never seen them in abundance until spending a week on Cypress Island recently.
Cypress Island is not far from Anacortes, Washington in the San Juan Islands.
A century ago, Cypress Island bustled with mining, logging, and other commercial activity. No longer. As far as I know, the island has a winter population of near-zero (plus a floating fish-farm in a cove).
In the 1980s, a developer acquired many square miles and planned a large-scale resort. Considerable opposition developed. Finally, the State of Washington (with help from a land trust) bought the land. The State turned much of it into a preserve.
I was there recently as an assistant crew leader on a Washington Trails Association crew. We criss-crossed the island doing trail work. The hiking trails are popular among kayakers, boaters, and campers.
Everywhere I looked, there were Douglas maples. They grew at the shoreline. They grew inland. They grew on the hills (1,000'/300m).
Big ones, too. They were second-growth trees, with many at 1'/30cmDBH [diameter at breast height].
Douglas maples are not tall enough to form part of the forest canopy. But they are higher than the understory.
On Cypress Island, they occupy an intermediate level between Douglas-firs and grand firs, on one hand, and salal, red elderberry, and vine maple, on the other hand.
As far as I know, Douglas maples prefer a somewhat drier climate than is typical of western Washington.
I got the impression that Cypress Island might be at least partly in the rain shadow of the Olympics.
Do you know whether Douglas maples are abundant elsewhere in the San Juan Islands?