I need a loop!

Wonderland Trail around Mt. Rainier.

Yep, +1 to the WT. The crowds are controlled by permits. You might see dayhikers near roads but interior wise, no.

There’s book about Mt Rainier that made me want to do the Wonderland Trail someday. (The author attempted and failed miserably, but the book was great, IMHO)

Measure of a Mountain.

Wonderland, the JMT and GC Rim-to-Rim and the top 3 trails on my to-do list for the coming years.

I don't know much about OR or CA, but a couple of books that come to mind for WA state are "Best Loop Hikes Washington", and "Trekking Washington". Both of these are Mountaineer books. You might be able to find these through your library system (don't forget "interlibrary loan"), or maybe a second-hand (or even first-hand) bookstore.

The Loop hikes book tends to have lower distance trips, the longest I recall in there was in the 40's of miles. The "trekking" book is better, but not all are loops — still, a number of them are, or at least "near loops" (i.e., not a long shuttle). This author defines "trekking" to be trips of 30-miles or more, and there are some nice looking options in it.

Of course I agree on the Wonderland trail being great, but it's something you have to plan ahead for and be ready with your permit application the day they open for that. There are other mountains you can walk all the way around, such as Adams, Glacier, St. Helens, probably others.

Bottom line is I would get a copy of the "Trekking" book if you're able to.