Most of what the Hohokam grew is gone. Corn, beans, squash and cotton are annual crops, and annual crops don’t outlast the people who plant them. One Hohokam crop did. On a few dozen benches above desert washes in central Arizona, clumps of a blue-green, pale-banded century plant still grow next to tumbled rock piles and old house sites. Botanists call it Agave murpheyi, the Hohokam agave. Arizona’s state heritage program lists the McDowell Mountains in its range.
This note covers what that plant is, how the rock-pile fields that grew agave worked, and why you won’t find a map here. The early history is in our chapter on Scottsdale before 1450, and the people behind it are profiled as the Hohokam canal builders.
Farming without a river
The famous Hohokam story is canals: hundreds of miles of hand-dug ditches carrying Salt River water across the valley floor. North Scottsdale had no river to tap. The City of Scottsdale’s archaeology overview, Ancient Peoples in Scottsdale (2003), describes a third kind of farming, alongside floodwater and canal farming, called dry farming: “used in upper desert areas of Scottsdale that were not close to any source of water, such as a river or large wash.”
Dry farmers caught rain where it fell. The city’s overview lists the tools: “check dams across small wash bottoms (built perpendicular to the channel), contour terraces along slopes, catchment basins, rock piles, and bordered gardens.” Rock piles “are found most often in combination with check dams along a wash.” It has found evidence of dry farming at Pinnacle Peak Village and at Spur Cross Ranch near Cave Creek. And “in the later Hohokam periods (Sedentary and Classic) check dams and rock piles were used to grow agave.”
The city’s 2015 Cultural Resource Master Plan for the McDowell Sonoran Preserve says the same at a larger scale. Hohokam communities in the region built “extensive agricultural rock pile fields in upland and bajada locations for cultivation of xerophytic plants (e.g., agave and cholla).” Its list of site types found in the Preserve includes “rock pile with ashy fill,” a likely roasting pit.
How a rock-pile field worked
The best description of these fields comes from the Tucson Basin, not Scottsdale. In the 1980s archaeologists Suzanne and Paul Fish and their colleagues mapped the Marana Community northwest of Tucson and showed that the Hohokam grew agave on a large scale. Their 1992 chapter, “Evidence for Large-scale Agave Cultivation in the Marana Community,” is the standard account.
- The piles. Fields were “marked by rockpiles and low stone alignments” covering “many hundreds of hectares.” The piles were rounded heaps of cobbles gathered from the bajada. They were rarely more than 1.5 meters across, and the cobbles often capped small mounds of soil.
- Why rocks. Rocks shade the soil and slow evaporation. When the team compared roots under rock piles with nearby bare ground, root weight under the piles averaged 80 percent higher. Planting experiments showed the rocks also kept rodents from digging at the base and roots.
- The tools. Two kinds of stone tool turned up all over the fields. One was a thin, flat “agave knife” made from naturally tabular rock, used to cut leaves from the heart. Microscopes have found calcium oxalate crystals like those in agave tissue on such knives. The other was a steep-edged “pulping plane” that stripped spines.
- The ovens. Roasting pits “filled with ash and fire-cracked rock” were found in many fields. An agave stores sugar for 5 to 20 years to fuel a single flowering. Cut just before it bolts and bake the heart in a pit, and you get a sweet, high-calorie food.
- The yield. In one zone of Marana, more than 485 hectares (about 1,200 acres) of large fields date to the early Classic period, roughly the 1100s and 1200s. The Fishes estimated those fields could have supplied about 20 percent of the calories for 775 people. Roasted hearts provide 347 calories and 4.5 grams of protein per 100 grams.
Agave had other advantages. It needed no canal, and it was harvested just before the flower stalk shoots up, which in this species starts in winter, a season when little else was ready. A rock-pile field on a dry slope may also have been a hedge against the years when floods wrecked the canals.
The plant that outlived its farmers
Agave murpheyi was formally described by F. Gibson in 1935 from plants along Queen Creek near the Boyce Thompson Southwestern Arboretum, outside Superior. Its oddities make sense once you see it as a domesticated crop.
According to the Arizona Game and Fish Department’s heritage abstract for the species, last revised in 2003:
- It almost never sets seed. Flowers form and then abort. It spreads by pups from the base and by bulbils, tiny plantlets that grow on the flower stalk, which “always” appear after flowering. A plant that can’t reproduce sexually behaves like a cultivar: it goes wherever people carry it.
- It grows “on benches or alluvial terraces on gentle bajada slopes … with pre-Columbian agricultural and settlement features,” and near rock piles. Its elevation range is about 1,300 to 3,200 feet.
- Its Arizona range includes “Paradise Valley (Phoenix Basin), McDowell, New River, and Wickenburg Mountains” in Maricopa County, plus sites in the Tonto Basin, the Verde drainage and around Superior.
- It may be one clone. The Arizona-Sonora Desert Museum, quoted in the abstract: “All of the populations from Caborca, Sonora, to New River, Arizona, are so similar that they may be one genetic clone.”
- There aren’t many. Desert Botanical Garden botanist Wendy Hodgson counted 35 to 40 known sites in 1991 and 60 by 1995, each perhaps with fewer than 50 genetically distinct plants.
The Tohono O’odham and ranchers in Sonora still grow it in yards and gardens, the abstract says. In Sonora people often say their yard plants came from “nearby hills.” Hodgson suggested why it vanished from the Phoenix and Tucson basins: once the farming communities broke up, nobody tended the plants, and the last century of development took much of the land they grew on.
How much survives in the McDowells specifically isn’t public. The Game and Fish abstract lists the range. Maricopa County’s 2019 plan for McDowell Mountain Regional Park puts the Hohokam agave on its special-status list as a plant that “may be found within the Park or conditions exist that may support” it. Our history chapter says the plant “still grows wild in the McDowells.” The state abstract supports that at the scale of the range, not any particular slope.
Why there are no directions
Three reasons.
The plant is protected. Under the Arizona Native Plant Law, Agave murpheyi is Highly Safeguarded, the strictest category, which means no collecting. The Forest Service and the BLM list it as a sensitive species. It was once a candidate for federal listing, and a petition to list it as threatened was turned down. The abstract names “illegal collection for cultivation and products” as a threat.
Where the plant grows, there’s usually an archaeological site. The agave grows on the old Hohokam fields and next to the rock piles, roasting pits and house sites that went with them. The abstract notes that the plant is “protected as an antiquity under the State Antiquities Act” when it grows with rock alignments and artifacts at prehistoric sites. Rock piles look like random cobbles to anyone who doesn’t know what they are, and a hiker restacking one is destroying a centuries-old field. The Preserve’s cultural resource plan keeps site locations confidential. Our note on Preserve rock art explains the laws, which cover rock piles as fully as petroglyphs.
The data is flagged sensitive. The state heritage abstract is marked “Data Sensitivity: YES.” Game and Fish doesn’t publish the locations, and neither will we.
Where to see the plant legally
- Botanical gardens. The Desert Botanical Garden in Papago Park is where much of the modern research on Hohokam agave was done, by Hodgson among others. The Boyce Thompson Arboretum near Superior is the species’ type locality. Plants from the original collection were cultivated there, though the state abstract says it’s uncertain whether today’s plants are the same clone. Collections change, so call either garden before you go and ask whether a specimen is on display.
- On the trail, by accident. If you’re hiking an official Preserve trail and see a clump of closed, spoon-shaped green rosettes with pale cross-bands and short spines, look and enjoy it. Don’t post the location, don’t pick bulbils, and don’t step off the trail for a closer look.
What’s still unknown
Nobody has published a count of Hohokam agave plants or rock-pile fields in the Preserve. Nor has anyone published whether the McDowell plants are the same clone as those near New River, or how many of the Preserve’s recorded sites are agricultural rather than habitation. The people who know are at the Desert Botanical Garden, the Arizona Game and Fish Department’s Heritage Data Management System, and the City of Scottsdale’s Preserve staff. Whatever they know has stayed off the internet, and that’s deliberate.
Sources: Arizona Game and Fish Department, Heritage Data Management System, Agave murpheyi plant abstract (revised 2003); S. K. Fish, P. R. Fish and J. H. Madsen, “Evidence for Large-scale Agave Cultivation in the Marana Community,” in The Marana Community in the Hohokam World (University of Arizona Press, 1992); City of Scottsdale, Ancient Peoples in Scottsdale (archaeology context, 2003) and Draft McDowell Sonoran Preserve Cultural Resource Master Plan (2015); Maricopa County, McDowell Mountain Regional Park Master Plan Update 2019–2039.