The geology of Arizona is all about upheaval, much of it volcanic in nature. It’s true that there are some relatively flat valleys (Phoenix resides in one, much of Tucson in another), but it’s also true that you can drive a hundred miles and go from the concrete thermal sump known as Phoenix to the misty aerial retreat of Pinal Peak.
Consider this pertinent elevation chart:
Phoenix – 1,080’
Apache Junction – 1,750’
Florence Junction – 1,883’
Gonzales Pass – 2,651’
Boyce Thompson Arboretum – 2,400’
Top of the World – 4,600’
Globe – 3,400’
Pinal Peak – 7,800’
As the chart indicates, Arizona topography is often a roller coaster. This chart also places Boyce Thompson Arboretum between the lowlands of Phoenix and the highlands of the Pinal Mountains. We are high enough to get some frost in the winter, but not quite high enough to laugh off the summer heat. From our vantage point, we can also watch each season roll by like a desert wave.
A good example of this metaphoric wave is when palo verde trees (and, simultaneously, mesquites) burst out in splays of yellow starting mid-March in Phoenix. Two weeks later, the palo verdes at Florence Junction start blooming. And by mid-April, the trees are blazing gold here at the Arboretum. In other words, it takes about one month for spring’s floral tsunami to climb over Gonzales Pass and flood down across the Arboretum. (That wave, by the way, tends to crash against Superior and spin slowly around in an eddy. Alas, you can only carry a metaphor so far.) In this part of the Sonoran Desert, all flowering plants bloom in much the same way, rippling across the rising landscape and slowly climbing the fractured hills until they wash out on elevation’s gradual incline.
- T. Stone