Route 66 Trip & More with Italian Visitor

[sgherardi]

Looking for all the help I can get here. I have a cousin in Italy that would like to visit the US for the first time this summer. We are interested in doing a Route 66 trip, wanting to see as much as possible. I think it is important to note my cousin's degrees and interest in geology. So, I'm looking for help planning a Route 66 trip that consists more of monuments, geologic sites, etc. than things like "Worlds Biggest Rocking Chair." Don't get me wrong, the silly fun stuff will be great little stops along the way; I just don't want them to be the focus of the trip, since this will be a first (and possibly only) trip to the US.

We definitely want the side trip to the Grand Canyon, and I think Vegas and the Hoover Dam would be good stops as well. What else would be mostly on the way? Interested in caves, hot springs, waterfalls, mountains, national parks, etc.

After reaching LA, I'm thinking about swinging up to San Francisco, Redwoods, the Treesort in OR, Breitenbush, and Olympic National Park, but I'm worried that I'm trying to pack too much into approx. 20 days... and I'm a little disappointed that this plan doesn't have time for NYC, the Smithsonian, etc. Obviously, I've never planned a road trip before.

Also, I'm not sure if this will help at all, but more details include:

20 days Summer 2013
2 travelers
27/28 yrs old
up for adventure (zip lines, hiking, kayaking, etc.)
enjoy the outdoors but also up for some city nightlife

Alright, what advice do you have for me?