University of Arizona

Sense of Place

Geos. 195D

Tucson Mts.

The Tucson Mts. is one of the favorite natural-cultural history short trips of Tucson. It has everything: geology, climate, desert plants and ecology, past and present cultures, pollination, pack rats, mining, sunsets, and more.
Snowy Tucson Mts., February 20, 2013. Paul Sheppard

Trail's End Rock Jumble

Trail's End has about 10 different kinds of rocks in one place. How so much variety in geology?

Paul Sheppard, 2009

Balloon rides in a deeply blue sky.
Ellie Oligmueller, 2012

New geological block model showing formation the
Tucson Mountains. Starting point (70 mya, left) and
ending point (today, above).
Photos — Paul Sheppard, 2014

Gary demonstrating the block model in video (3:32 minutes)


Jojoba, leaves and male flower
Caige Dominici, 2017

Native to the Sonoran desert, this abundant plant is interesting biochemically such that various attempts have been made to cultivate it. Is cultivation working?

Whatever happened to jojoba?: This 1990 Arizona Highways article sums up jojoba cultivation at that time. (password protected)

Male flower, emitting pollen

Female flower, catching pollen
Male and female flowers exist on separate plants. Pollination is by wind, so pollen from male flowers must waft over female flowers for fertilization to occur. The upright stance of leaves helps facilitate this.
Jojoba Fun

Fitz, Arizona Daily Star

Brandon Groom, 2019

Giant Saguaro

We'll check out saguaro quite closely, including right next to the spines.
Maybe we'll get lucky and see a bobcat "treed" up one of the giants.

Saguaro spines up close.
Paul Sheppard, 2009

Saguaro Skyscraper.
Paul Sheppard, 2011

Saguaro top up close.
Gaizka Urreiztieta, 2011

Saguaro, old and new.
Meghan Marriott, 2014

Saguaro diameters on a daily basis.
(click to see hi-res version)

Paul Sheppard 2015
Cristate (Crested) Saguaros:
Ash Abbate 2023

Paul Sheppard

Paul Sheppard
Recent hard freeze likely will be death knell for many weaker saguaros: This 2011 AZ Daily Star article notes potential mortality of saguaro due to the cold snap early February 2011.

Sonoran desert may be coming apart at the seams: This 2012 AZ Daily Star article covers research on plant response to current warming.

PBS 2022: State of the state of Saguaro cactus: Saguaro in the face of climate/ecological change.

A saguaro commencement address: This 2014 AZ Daily Star op-ed by David Fitzsimmons gives sagely saguaro advice.
Fitzsimmons: Saguaros like
nurse, "mom," trees.

Gates Pass

Gates Pass, within Tucson Mountain Park, has volcanic rock of the Tucson Mt. Caldera as well as outstanding vistas of more saguaro and more Basin and Range.

Tucson Oddity: Look up, down, all around: This 2012 AZ Daily Star article explains the stone structures at Gates Pass.
Civilian Conservation Corps buildings endure at Gates Pass: This 2015 AZ Daily Star article explains more on the CCC structures at Gates Pass.
click to enlarge

Fist-sized limestone in Cat Mountain rhyolite.
Colleen Mathis, 2010

Gate's Pass, grand vista of Basin and Range.
Paul Sheppard, 2017

Avra Valley dust storm. Paul Sheppard, 2011

Cat Mountain Rhyolite cliff face. Paul Sheppard, 2020

Arizona-Sonora Desert Museum

SOP does not stop at the Arizona-Sonora Desert Museum (we pass by it), but it's internationally renowned and well worth visiting. For example:

Raptor Free Flight

Bighorn Sheep

Cholla Forest

  • ASDM News: Native Bees. A 3-page article on native bees of the area.

Saguaro National Park

SOP visits Saguaro National Park, specifically the West Unit.

click to enlarge

click to enlarge

click to enlarge

Sus Picnic Area

Sus Picnic Area has new rocks, new minerals, new plants, new animals, and outstanding vistas. Click here to read and hear about copper mining in Arizona (one of Arizona's famous five C's).

Jayme Kelter, 2007

Rattlesnake, out already by late January?
Paul Sheppard, 2012

Ocotillo leafing out already
A.J. Di Domizio, 2012

Sus Panorama, 2016

Stormy Sus, 2017
Photos — Paul Sheppard

Packrat midden at Sus

Cholla patch at Sus

Mining in Southern Arizona

Mining has been key economically to Arizona, especially mining of copper, one of the "Five C's" of Arizona. Humanity needs copper and mining provides jobs, but copper mining leaves a mark environmentally.

The cement mine, right near I-10, viewed from Signal Hill. Paul Sheppard, 2018

Sus test pit rock, with blue copper.
Paul Sheppard, 2015

Aerial view of Silver Bell Mine (copper),
just northwest of the Tucson Mts.
A new copper mine, called Rosemont, is proposed for the east side of the Santa Ritas, between I-10 and Sonoita. The debate about this proposed mine includes the usual pros and cons. Start with the wiki page and continue from there as desired.

Low copper prices delay Rosemont Mine: March 2016, an update on the Rosemont.

View of the site where the Rosemont Mine would go, currently a mixture of mesquite-ocotillo grassland, Madrean oak woodland, and piñon-juniper forest,
with SOP alumni for framing. Paul Sheppard, 2017
View of the site where the Rosemont Mine is going (test digs circled in red), still a mixture of mesquite-ocotillo grassland, Madrean oak woodland, and piñon-juniper forest. Paul and Melissa, 2022
Newsclips about mining in the Tucson Mountains: See also:

Petroglyphs (Rock Art)

Signal Hill is aptly named, as it has many ancient petroglyphs, i.e., images tapped into rocks. Who? Why? How long ago? What do they mean?

Jayme Kelter, 2007

Gaizka Urreiztieta, 2011

Meghan Marriott, 2014

Carly Stewart, 2014

Caige Dominici, 2017

Nina Kolodij, 2015

Brandon Groom, 2019

Signal Hill is very popular along the Tucson Mountains circumnavigation (2019).

Cholla Cactus of the Sonoran Desert

Nina Kolodij, 2015

Paul Sheppard, 2016

Close up. Paul Sheppard, 2016

Barrel Cactus of the Sonoran Desert

Adobe Stock

Adobe Stock

Peanuts archive

The Sonoran Desert Larder

Chef Gary's Nopalitos Horneados
(baked prickly pear pads)

1 pad fresh nopal, the fleshy part of prickly pear cactus
some cooking oil
a pinch salt
  Dethorn and wash (rinse) nopal. Pat dry with paper towel. Slice and/or dice as desired. In mixing bowl, add oil and salt to nopalitos and stir. Place on cookie sheet and bake at 400º F for 15 minutes. Serve warm, room temperature, or chilled. Good with tortilla chips or as toppings on other Sonoran dishes. ¡Que sabroso!

Paul Sheppard, 2014

Partaking of the Sonoran Desert larder.
Gary Huckleberry, 2017

Gary's tepary beans (2019)
(another lugume, by the way)

Sunset in the Tucson Mountains

Southern Arizona is renowned for spectacular sunsets. West side of the Tucson Mountains is especially good for viewing sunsets.

Signal Hill, May, 2013. Paul Sheppard
(the flying speck is a Lesser Nighthawk)

Signal Hill, May, 2013. Martín Hadad

Gilbert Ray, January 29, 2017. Paul Sheppard

Gilbert Ray, January 29, 2017. Paul Sheppard

Legume Trees of the Sonoran Desert

The uniqueness of the Sonoran Desert is due in large part to its trees, most of which are legumes, i.e., in the Legume botanical family, home to renowned favorites like peanuts, beans, and peas. Here are four common legume trees of the Sonoran Desert:



Palo Verde

Legumes provide an invaluable service to life on Earth: They support soil bacteria that fix nitrogen, which means converting N2 gas of the atmosphere, which is unusable by most life on Earth, to the usable, reduced form of ammonia (NH3), which converts further to the ionic forms of ammonium (NH4+) and/or nitrate (NO3), which are usable by, if not indispensible to, life on Earth. Some reading:

Ironwood Forest National Monument

Just northwest of Saguaro National Park lies a lesser-known desert park called Ironwood Forest National Monument. Wild Sonoran Desert, primitive camping, sublime solitude.

Ragged Top Mountain.

Bring firewood (but local, not exotic)
to avoid depleting the desert.

Great sunsets, as usual for southern Arizona.

Ironwood tree, the namesake.

Panorama of Sonoran Desert from slopes of Ragged Top. What a desert!

Sus Team Photo, 2024

Paul Sheppard, 2024

Back to Sense of Place Home Page

Laboratory of Tree-Ring Research, University of Arizona
Tucson, Arizona 85721 USA
Comments to Paul Sheppard: sheppard @