You can do 500 a day, easy:
3 days, 1450 miles:
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That said, that was one of our more aggressive trips. As geocachers and hot springers, many days might be 100 to 150 miles, depending on our objectives. We've had a few 0 mile days too....
You'll figure out what is comfortable for you. Start small - plan on 200 to 250 tops, then adjust from there.
Stop often, take lots of pics, take in the sights, enjoy the journey. You may be looking for adventure, and you might just find it! Some people try to avoid adventures, but the adventure finds them.
RV/Cache/Soak On!
(Pics of a few of our adventures...)