I am going on vacation with my parents for their 30th anniversary celebration. We are going to be headed to Denver, Salt Lake City, and Yellowstone for sure. Any thing we need to see for sure? Any tips? Best routes to drive? Also, we will be using my T2i. What lens should we purchase for the trip? I was thinking the EF 100-400mm f/4.5-5.6L IS. Thanks in advance!