The University of Arizona

2500 years on Tumamoc Hill

ca. 2500 years ago

Indigenous peoples build a town on the mesa at the top of Tumamoc Hill. They surround it with a trinchera, a massive, rubble-laid wall of native volcanic rock.

ca. 1500 years ago

The upper town is abandoned as a residence site and it becomes a place of ceremony and pilgrimage.

Pre-Columbian millennium

Extensive Hohokam settlement and farming occurs at the base of the Hill, including an agave plantation on the plain SE of Anklam and Greasewood roads. The Hohokam leave extensive relics all over the area, including handsome petroglyphs and pottery fragments.

ca. 1450

The Tohono O'odham people (descendants of the Hohokam) move their area of settlement southward away from Tumamoc, but they and other Arizona tribes maintain their spiritual connection to Tumamoc Hill.


The Mission San Agustin de Tucson is established on the west bank of the Santa Cruz River near Tumamoc Hill.


Hugo O'Conor establishes El Presidio de Tucson east of the Santa Cruz River. The modern city of Tucson is born.

ca. 1858

Cattle grazing begins on and around Tumamoc Hill. Goats, burros and horses also graze freely. Soon, quarrying of Tumamoc's basalt begins to supply Tucson with native rock for building homes, walls and other structures.


The Southern Pacific Railroad reaches Tucson. Railroad executives appeal to the bishop of Arizona for a hospital in Tucson. The Sisters of St. Joseph of Carondelet establish St. Mary's Hospital at the foot of Tumamoc Hill.


Frederick V. Coville visits Death Valley and is intrigued by its varied plant life (Science 20: 342). He wonders how plants could possibly manage in such heat and aridity.


With the blessing of President Theodore Roosevelt, Andrew Carnegie founds and endows The Carnegie Institution to conduct scientific investigations. Coville, now the Botanist of the US Dept. of Agriculture, appeals to the Institution to set up a botanical laboratory in the desert. Purpose: to discover how plants manage to survive and thrive in hot, dry environments. The Carnegie sets aside $8,000 for the lab and delegates Coville and Daniel T. MacDougal to find a suitable place for it.


 After an overland journey that takes them to promising sites in California, New Mexico, Chihuahua and Sonora, as well as Arizona, Coville and MacDougal choose Tumamoc Hill and its surroundings as the site for the botanical laboratory. The Tucson Chamber of Commerce arranges to buy and lease 880 acres as a scientific reservation for The Desert Botanical Laboratory. W.A. Cannon becomes the Lab's first resident director. Its first building ready, The Desert Botanical Laboratory opens on 7 October. Prof. Volney M. Spalding of the University of Michigan visits the DBL and asks to be allowed to work there. Spalding is a noted forest conservationist and taught the world's first true forestry course at Michigan in 1881. He is also a botanist and wants to contribute to the investigation of how plants get along despite desert heat and dryness.


The Carnegie Institution of Washington is chartered by the Congress of the United States of America.


Desert plant physiological ecology is born on Tumamoc. It continues to be practiced here to this very day. The very first Tumamoc research paper is published: Volney M. Spalding, 1904, Biological relations of certain desert shrubs. I. The creosote bush (Covillea tridentata) in its relation to water supply. Botanical Gazette 38: 122-138. The first review of the plant physiological work is Burton Edward Livingston's (1906. The Relation of Desert Plants to Soil Moisture and to Evaporation. Publication No. 50, The Carnegie Institution of Washington, Washington DC).


Mrs. Effie S. Spalding, an accomplished botanist in her own right, publishes her first research paper done on Tumamoc (Spalding, Effie S. 1905. Mechanical adjustment of the sahuaro to varying quantities of stored water. Bull. Torrey Botanical Club 32: 57-68). She shows that the stems of saguaro cacti expand when water becomes available, and contract as it is used. That explains why the stems of saguaros, as well as many other cacti, are pleated like an accordion.


Francis E. Lloyd, plant anatomist at Columbia University, buys a struggling magazine of popular botany, The Plant World, and becomes its editor.


During the springtime, Volney Spalding sets out 19 perennial plant quadrats, each 10x10m, maps all their individuals, and photographs them. He puts them in every discernable habitat in the Tumamoc reservation. Today, nine of these plots remain, and a tenth, which was partly destroyed by a thoughtless roadbuilder in 1948, has a well known location, has a set of intermediate censuses taken more than 40-years ago by Ray Turner, and will soon be restored. Spalding's permanent plant quadrats are the world's oldest.


The Tumamoc Ecological Reservation becomes a restoration ecology project, the world's first. To protect Spalding's growing vision of Tumamoc as a place to observe the recovery of natural vegetation and to embark on a long-term study of the structure and function of plant associations in the complex desert landscape of Tumamoc, The Carnegie funds a 5-mile-long, barbed-wire fence to encompass the entire 880-acre reservation. Grazing ceases. Quarrying is also halted. "Within a few months after the completion of this fence" the investigators notice a change in "the vegetation and that of the surrounding areas..., and also an increased abundance in the number of the wild animals." To help Spalding's investigations, Prof. Tolman, University of Arizona, and his students, map the entire reservation, and Prof J. J. Thornber, University of Arizona, gives the Lab a set of herbarium specimens.


Francis Lloyd and his wife Mary move to the Desert Laboratory, bringing The Plant World along. In a few months of research, Lloyd produces a book, The Physiology of Stomata, which stands for a half-century as the explanation for how plants open and close their stomata — the tiny holes in their leaves that allow them to take in CO2 and release O2. It remains part of our understanding to this day!

The Lloyd residence at the foot of Tumamoc Hill. Mary -seen here- is pregnant!



Lloyd leaves the DBL in 1907, leaving his journal and its mounting debts behind. Livingston becomes its editor and MacDougal, now resident director, undertakes to put the journal on a sound financial footing. The Plant World becomes the journal where much of Tumamoc's research is published.


Spalding becomes editor of The Plant World.


Spalding, with the help of a poor guy named Jacob Blumer, sets out to tag and map every last giant cactus on the reservation. During the first year, they succeed in doing between 10,000 and 15,000 saguaros. Blumer quits, unappreciated, and the effort is scaled down to four large saguaro plots, which have been studied periodically and remain today. Spalding finds very few saguaro seedlings on Tumamoc and worries about the future of the species. His concern eventually leads University President Homer Shantz to begin saving land on the west side of the Rincon Mts. that was dense with saguaros. The project expands to become Saguaro National Park. Meanwhile, after decades of observation on Tumamoc, we learned that saguaros hardly ever reproduce. Not to worry, a good year did finally arrive, the cactus flourished and Arizona breathed a sigh of relief.


Forrest Shreve takes the baton from Volney Spalding. He becomes editor of The Plant World and agrees to continue collecting data from the permanent quadrats.


Shreve adds a 557m2 permanent study plot (still used occasionally) and censuses its perennials.


About 50 ecologists meet in Chicago and found The Ecological Society of America. Seven of them are investigators of The Desert Laboratory.


The Ecological Society of America takes over The Plant World from Shreve and The Desert Laboratory. It becomes Ecology. Until 1954, the masthead of Ecology proudly acknowledged: "CONTINUING THE PLANT WORLD."


Shreve sets up another eight permanent quadrats in the bajada southwest of the mesa where he found soil different from any included in other quadrats. Still used, these quadrats are adjacent to each other, forming equal 10x10m subdivisions of a 20x40m rectangle.


A few Desert Laboratory stalwarts take lunch at the Old Pueblo Club on 7 October to celebrate the thirtieth birthday of the laboratory. Indicative of the Great Depression and diminished support from The Carnegie Institution, no one else attends.


Tumamoc grants its first public utility easement. The forerunner of today's El Paso Natural Gas Co. builds a major pipeline through southern Arizona to deliver natural gas to the region for the first time. It traverses some 1,800 feet of the reservation. Shreve is unhappy but finally relents after obtaining some needed adjustments to the easement. The EPNG of 2008 has become a valued partner of Tumamoc in resolving issues that threaten research on the reservation.


The Carnegie sells Tumamoc to the US Forest Service for $1, but it had not forgotten its mission nor entirely abandoned its advocacy. The President of The Carnegie, Dr. Vannevar Bush, to C.L.Forsling, Asst. Chief, US Forest Service (16 Mar. 1940): "The Institution wishes to stress the desirability of maintaining the fenced-in land as a demonstration area of natural conditions for future studies." This in response to a Forsling to Bush letter (20 Feb. 1940): "...the Forest Service would immediately assume custodianship and protection of the entire area of some 900 acres. Its policy would be to keep the area enclosed and otherwise protected from domestic livestock use."


Under the aegis of the US Forest Service, the reservation gets little use. The few studies done are accomplished by University of Arizona faculty and students. Meanwhile USFS invites the US Marine Corps to build and use training facilities on Tumamoc Hill. It also re-establishes quarrying in the form of a clay pit for brick making, allows the construction of damaging roads, and - especially in the 1950s - indulges in a flurry of easement-granting that has left the reservation scarred and damaged the remains of the ancient village on the mesa top. But, they did maintain that fence, just as they had promised! We are still The Tumamoc Ecological Reservation.


The University of Arizona buys Tumamoc and assumes responsibility for the reservation. In the deed, the UA promises to use it solely for research and education.


The US Secretary of the Interior designates the Desert Laboratory a National Historical Landmark. Volney Spalding's quadrats and three of the laboratory buildings are listed in the designation.


The State of Arizona designates Tumamoc Hill as a State Scientific and Educational Natural Area for its biological excellence.


The US Secretary of the Interior extends Tumamoc Hill's National Landmark designation to cover the entire 860-acre ecological reservation.


Governor Rose Mofford officially sets aside 200 acres of State Trust Land on behalf of The University of Arizona to use for research. This land - part of the original land grant received by the University when it was established - had always been within Tumamoc's fenced border.


Centennial - The Desert Laboratory is 100 years old.


Joaquin Ruiz, Dean of the UA College of Science, forms The Alliance for Reconciliation Ecology on Tumamoc Hill. The Director of the Alliance, Michael Rosenzweig, is also charged with the responsibility for directing the Desert Laboratory.


Dean Ruiz creates an umbrella called Tumamoc: People and Habitats. Its divisions are The Desert Laboratory; The Alliance for Reconciliation Ecology; and the archeological activities plus cultural obligations incumbent upon a University that fully respects the past and its treasured legacies.