Interstate 8 CA-AZ to see some pretty ones.
But this is what one end of Interstate 8 looks like in California. The other is mountains out of San Diego, and in between is the very flat farmland area of Imperial County, where much of the fruit and veggies you eat from California come from in the winter. That area has been heavily irrigated from the Colorado River for years. Nowadays there are agreements to send on some of the water to San Diego, so the farmers are working out more efficient methods for transporting and using the water! Some of the water goes on to Mexico, where it is also used for irrigation, so the Colorado rarely reaches the Bay of California any more.
We crossed the Colorado going out at Yuma (there's a picture in the set) and coming back at Blythe on Interstate 10. And of course we saw it several times at the Grand Canyon. (That's not easy - there are so many rocks in the way, you have to be in the right position!)
But of course, being here at the border, maybe I should muse about the people who cross the border against the flow of the Colorado. They must really want to come, if that's the way they try to enter. But I'll save that topic for another time.