Driving across the Midwest, I am always impressed with the extent of the grasslands and really enjoy the beauty of the southwest as we get into New Mexico and Arizona. We had been driving through grassland for a long time and then start to get into hills with pinyon-juniper woodlands.
We crossed through historical tallgrass prairie, shortgrass prairie, and then into the arid southwest with high plains area and then finally dropped down into the Sonoran desert with its iconic Saguaro cacti. Much of these changes is controlled by the moisture gradient across the west due to the rain shadow from the Rocky Mountains (Brady, N.C and Weil, R.R. 2008. The Nature and Properties of Soil. Fourteenth Edition. Pearson Education).
This gradient also controls the soil orders across the US. We started our drive across Illinois seeing dark black soils that are Mollisols. As we drove across Texas we saw deep red soils from the B horizon that likely had a lot of iron (Brady, N.C and Weil, R.R. 2008. The Nature and Properties of Soil. Fourteenth Edition. Pearson Education).
The San Francisco Peaks (above Flagstaff Arizona) are 12, 633 foot tall peaks on the Colorado Plateau that are an old stratovolcano. Around the base of the mountains is a Ponderosa pine forest and then it grades up to a spruce-fir forest at the top of the mountain.