I was working on my new book – “An Illustrated Guide to the Santa Catalina Mountains” and wanted to know just how old these mountains are. Different books gave different dates. My favorite article was: “A Guide to the Geology of the Santa  Catalina Mountains, Arizona”
by John v. Bezy of the Arizona Geological Survey, which taught me that this is not at all a simple question. The oldest rocks (called Pinal Schist) in the Catalina mountains date back 1.65 billion years.

The process that started to shape the Catalina mountains as we know them went through several phases. The main upheaval that forms the core of the mountain range goes back about 35 million years in the Cenozoic age when the super continent known as Pangaea was further separating and the Atlantic ocean was being formed.

There was more development 26 million years ago, and again 15 million years ago.

This means that this wonderful mountain range has been in the process of construction for twenty million years or more. And it is still changing. I seem to have read somewhere that it is still growing about an inch every hundred years, but have not been able to confirm that. In any case, it is a work in progress.

And as the mountain range itself evolves over the centuries and millennia, the plants that call it home have also been changing. For example saguaros arrived after the last ice-age which ended about 11,700 years ago.   We have the privilege of coming to know some of the plants that flourish here now. Who knows what the future holds?

Look for me at the Festival of Books at the University of Arizona Campus  –

March 10, 11 booth 254.

This painting is for the cover of my new book, and shows a profile of the mountains viewed from the South. The range is about 20 miles wide and a mile and a half high.