You have a choice of two in your Estes Park car wash, unless you can find a nice homeowner who will let you use their hose, or the cheerleaders are trying to raise money or something.
Shell 534 S Saint Vrain Ave, (970) 586-0193 A little bit south of downtown Estes Park on Highway 7. Both self service and full service washes available, and there is a vacuum too. Bring lots of quarters.
Eastside Center Car Wash 361 S Saint Vrain Ave Also south of downtown Estes Park on Highway 7. This is an unattended, coin-operated car wash with vacuums.
If you'll be traveling through Lyons on your way out of Estes Park, there is a self-serve car wash on the main street (there is a large mural on the side of it). If headed past Longmont on Hwy 66, turn right on Hover and go a few blocks to the Hover Car Wash (self serve). If headed through Loveland, there are several car washes along Hwy 34. If headed through Boulder, stop at Puddle Touch-Free Car Wash, on 28th Street/Hwy 36. If headed through Grand Lake, there is a self-serve wash at the entrance to town, by the Post Office.