It's about 400 miles to Sisters, Oregon from Everett. The Three Sisters mountain range is a little Southwest of there (pretty much due East from Bend).
I'm hoping for some nice weather in September or October otherwise maybe next summer when I can take a week - there are lots of interesting looking roads in that area that take you through forests, by rivers, lakes and mountains.
This is a snip from Sound Rider article about the McKenzie Pass-Santiam Pass Scenic Byway -
"Up one pass, down through the other, reverse the route and repeat as necessary! The town of Sisters makes a great start and ending point for this magical loop that offers it all. Fantastic scenery and some of the most technical riding you’ll ever encounter on public roads."
Here's a longer article Tails of the Three Sisters and the Google Map satellite image showing the Three Sisters -
McKenzie Pass is on Highway 242 and Santiam Pass is on Highway 20 on the map above.
Dee Wright Observatory is on McKenzie Pass.
Three Fingered Jack is north of Santiam Pass.