Why is our "Rocks of BTA" walk so enduringly popular? Even during the hottest summer months this geology tour consistently draws dozens of enthused attendees. One of our charming rock-jock tour guides may have said it best a few years back when interviewed: "Deep down we all know that geology is the most exciting subject on this planet—and perhaps all planets. Anyone with a basic understanding geology can look at any mountain that surrounds them and begin to understand the true diversity of nature and depth of time."
Then again, our charismatic guides are a draw: adventurous ASU Professor Steve Semken, plus two professional geologists, Scott McFadden and Rich Leveille. Tempe resident Steve Semken teaches geology and sustainability science and has been a professor at ASU since 2003. Geologic research has taken him around the world from New England to Inner Mongolia. We caught up with this globe-trotting geologist who says most of his most enthralling rocks and landscapes are right here in Arizona. He's a volunteer with the AZ State Parks system, guiding geology walks at Boyce Thompson Arboretum (check the updated schedule at http://ag.arizona.edu/bta/events.html) and included with $10 park admission.
Q. Why is Arizona a great place to be in your line of work?
The one-word answer is exposure. Our arid climate means that a lot of Earth’s crust is visible at the surface and easier to study! But what really makes Arizona unique is its magnificent diversity of landscapes, rocks, and ecosystems. It’s kind of like three states in one: northern Arizona and southern Arizona have very different topography and exposed rocks, as do the rugged central highlands lying in between. The Superior area, including the Arboretum, is especially interesting because it is located at the boundary between two of these major topographic regions, so there’s a lot of variation in a short stretch.
Q. Did you collect rocks when you were a kid?
Yes, from early on. I was born and reared in northern New Jersey. New Jersey has amazing geology, but most of it is covered up by vegetation or civilization! Luckily for me, my parents bought me a membership to a rock and mineral club, and I was able to take many memorable field trips and hikes into places where you could actually see and collect rocks, such as the Franklin mining district, which is world-famous. Many people don’t know that New Jersey was a hard-rock mining state for much of its history…it provided iron for George Washington’s army. Another key thing my parents did for me was to give me a big illustrated Golden Book of Geology, not long after I learned to read. That book made a huge impression on me, and I still have it on my office bookshelf.
Q. What's the focus of your research at ASU?
My primary field is called ethnogeology. It’s a new specialty that combines geology, geography, and anthropology. My students and I are very interested in learning how different cultures understand and interact with the Earth in their homelands. That research goes back to my previous job, teaching geology at the tribal college of the Navajo Nation. My students and I work mostly in the Southwest but also in some parts of Latin America.
One of our major goals is to use our findings to help encourage more diverse students to pursue careers in geology. Another is to use different perspectives to promote more sustainable living in our desert environment.
I also do geologic research in the field in northern and central Arizona with my students. You might be surprised to know how much more we still have to learn about the geologic history of our home state. I never get tired of teaching about southwestern geology.
Q. What are a few hobbies or interests outside of geology ?
Hmm…it’s kind of hard for me to separate work from hobby because most of my pastimes involve being outdoors in the deserts or mountains. And one of the perks of being a field geologist is getting paid to work outdoors in beautiful places! But I’m particularly fond of river rafting, camping, and hiking with my wonderful wife jeanne and our dog Sancho. BTA is a favorite place for the 3 of us to go. I don’t turn the geologist part of me off when I’m out on a hike or rafting a river for fun, and I appreciate jeanne’s forbearance (and interest) when I get a little nerdy at a rock outcrop now and then. Some of my other passions are cooking, wines, tequilas, and Sun Devil football.
Q. What are two charismatic rocks you point out on Arboretum tours?
All rocks are interesting to geologists because they tell stories about the Earth. I’d say the coolest rocks are the ones that are “in your face” with their stories—they have features that people can readily see and interpret. Among my favorites are the big freestanding blocks of grey schist near the Smith Building. Schist is a crystalline rock that forms deep in the crust and records the very origins of continents and mountains. You can see grey schist exposed as you drive through Gonzales Pass west of the Arboretum. That rock tells the story of the original formation of Arizona’s deep crust, about 1800 million years ago.
But I think the coolest rock of all at BTA is the volcanic breccia exposed in the bed of Silver King Wash where the Chihuahuan Desert Trail crosses. Breccia is made up of big chunks of rock expelled by a volcano and welded together. The breccia in Silver King Wash has fist-sized chunks of white pumice set in a matrix of tan volcanic ash. Rock like that is direct evidence of the violent volcanic eruptions that occurred locally about 20 to 18 million years ago and also formed the Superstition Mountains and Picket Post Mountain. I always end my geology hikes at that spot in the wash.