I wouldn't call them loops, but several scenic drives come to mind:
- WA20 itself is promoted as part of a big loop that includes US2 (2-3 day drive)
- east of Concrete is Marblemount, and the Cascade River Rd. About 10 miles of that is paved. It ends up the trailhead for an easy hike up to the Cascade divide.
- paved road north to the shores of Baker Lake. Not a loop.
- WA530 south to Darington. From Darington 530 goes west, past the Oso landslide, to Arlington. You complete a loop by going north on WA9 to WA20 and back east. Or, if up for some gravel road, take Mountain Loop Hwy SE and around to Granite Falls (and complete the loop to Arlington).
- a drive to Marblemount can be made into a loop by taking Rockport Cascade Rd back to 530. It runs on the south side of the river. But other than the fact that traffic is lighter, it doesn't have much to offer compared to 20.
- Concrete Sauk Valley Rd runs along the south side of the river from 530 to 9. A nice local road, but few big scenic views.
- WA20 to WA9 north to WA542 - not a loop, but a way to the north side of Mt Baker. Heather Meadows is high on the NE flank of that mountain.
- there are more drives at the west end of WA20 - Whidbey Island, Chuckanut Drive, LaConnor, etc, but Concrete is too far east to be a good base for those. But if I were to pick one base I'd choose Rasar State Park.
If you are up for gravel forest service roads and hiking there are more options in this area.
