The focus of Trip 4 is on geology and evidence of evolution, mainly in the form of fossils. The trip is named "Four Corners" because the sites are located in the four corners states of Colorado, Utah, Arizona and New Mexico.
The trip's first stop is Comanche National Grasslands in Southeastern Colorado. There you can experience one of the largest dinosaur track sites in North America.
Next, the trip plunges into the mountains and stops at the Florissant Fossil Beds National Monument, where fossilized insects and huge petrified sequoia stumps can be experienced.
From there, the trip pops back out onto the plains and into Denver for a museum stop, the Denver Museum of Nature and Science. While the optional museums in Lawrence and Hays, Kansas are pretty darn good, this one is truly world-class. Other world-class museums will be visited in trips 8 and 10.
Then it's all the way to the western border of Colorado to Dinosaur National Monument, where fossils can be experienced in their more natural state, as opposed to being cleaned up for a museum.
Then the trip focus shifts to geology as it visits the Grand Staircase Escalante, which includes Bryce Canyon, Zion and Grand Canyon National Parks. Combined, these sites show the most extensive record of geologic history on earth.
At Petrified Forest National Park, fossilized (or petrified) trees are again a focus.
Shiprock, in Northwestern New Mexico, presents another opportunity to experience geology in the form of eroded volcanic rock.
Finally, Mesa Verde shows evidence of human civilization in the relatively recent, but unrecorded, past. Evolution is about the process of change, and this site shows how things used to be for our species in one part of the world, and that things have obviously changed.
This series is about experiencing life. That is a double-entendre. Learning about biology, the study of life, is one aspect of that. The other aspect concerns the kinds of experiences that make up a full and interesting life. These experiences can be purely emotional, as opposed to the rational experiences and interpretations required of scientific learning. So another goal of the series is to distinguish between these two opposing, yet equally legitimate, ways of experiencing life. To that end, it may be helpful to read this short explanation of the position of Experiencing Life on a scientific theory that tends to provoke emotions in some people: On The Learning Of Evolution. Hopefully, after reading it, you will feel less threatened by the topic, and science in general, and can have more fulfilling experiences.