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Pueblo Grande MusemnProfiles No. 12

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Desert Canals:AHohokani Legacy

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Introduction\

Visitors to the Salt River Valley are often surprised todiscover a fertile agricliltural region flourishing in the aridArizona desert. However, these modernagricllitural ­achievements are not withouLprecedent. From AD 600'to 1450, the prehistoric Hohokarn constructed one of thelargest and most sophisticated irrigation networks evercreated using preindustrial technology. By'AD 1200, ­hlmdreds of miles of these watelways created greenpaths winding out from the Salt and Gila Rivers, dottedwith large platform mowlds. The remains of the ancientcanals, lying'beneath the streets of metropolitan Phoenix,are currently receiving greater attention from local.archaeologists. We are only now begimung to wlderstandthe engmeering, growth. and operation of the Hohokarninigation systems. This infOlmation provides new insightsinto the Hohokam lifestyles and the organization ofHohokarn society.

Early Records of the Prehistoric Canals

When the first explorers, trappers, and farmersentered the Salt River Valley, they were quick to note theimpressive ruins left by the Hohokarn. Villages containingplatform mowlds, elliptical ballcowts and trash mowldscovered with broken ceramic pots and other artifactseXIsted thr6ilghout the valley~Stretching out from theriver was avast system of abandoned Hohokarn canalsthat ran from site to site across the valley floor. In thenlid-1800s, the testimony of these ancient canals to inten­sive prehist0l1c irrigation, along with the success of thecontemporilly Pima Indian farmers, led Jack Swilling,John YT. SnUth and the early MOImon pioneers of theLehi settlement to begin the process of building a new

commwuty founded on irrigation agl1clliture.The ancient canals served as amodel for modern irri­

gation engineers, with the earliest historic canals beingformed largely by ~lealUng out the Hohokarn canals. Theancient !Uins and canals were a source'of pride to theearly settlers who envisioned their new agricllitural civili­zation risingas the.mythical phoenix bird from the ashesof Hohokarn society. The canals were usefW at times,being employed as wagon roads. In contrast, canaL~ creat­ed unwanted chalmels through areas being developed bymodern farmers. When afarmer purchased land, the area

, impacted by aprehistoric canal was often calclliated alldsubtracted from the purchase to offset the costs incurredby filling it.

As modern farmers began to fill in the tracesof theprehistoric callals, several prominent citizens becalneinterested in these prehistoric monwnents. They preparedmaps showing the locations of canals, villages and moundsthat fOlm the basis of Hohokarn scholarship today. JalnesGoodwin,alocal faImer, produced amap of the canals onthe south side of the Salt River in what is now Terrlpe,Mesa and Chandler. Herbert Patrick, a professionill carto­grapher and swveyor, mapped canals on the north side ofthe Salt River. In 1922, Gmar Turney, the City Engineerfor the City of Phoenix, used these early maps combinedwith his own knowledge of local prehistory to publish thefirst comprehensive map of the prehistoric ruins andCallalS of the Salt River Valley./The most extensive recordswere made by Frank Midvale, an' archaeologist whodevoted his life to recording the traces of the HohoKarn asthe remains of their cllitme were, destroyed by the rapidexpallsion of modern agriclliture ana urban growth.

The Development of Prehistoric Irrigationin the Salt River Valley

At about the time of Christ, people begall to moveinto the Salt and Gila River Valleys. Little is known about

~Pueblo Grande Musewn and Cllit.w·a! Park

these people who established the first small hamlets alongthe telTaces above the Salt River. They appear to havelived asedentary agricultural lifestyle, establishing fieldsalong the margins of the river. They probably relied onnoodwater farming teclmiques, planting in the wet soil in ,areas that had been inwldated when spring IUnoff swelled'the rivers beyond their banks. Perhaps as early as AD 50,these early inhabitants introduced a new teclUlology,canal irrigation. This technology would eventually givefOlm to the unique prehistoric culture of southern Arizonaknown as the Hohokam. Canal inigation was previouslyemployed by peoples living along rivers and smalldrainages in Mexico, although their canal systems neverattained the size and sophistication of the Hohokam canalsystems. The earliest Hohokam irrigation systems mayhave been small canals located close to the liver. til thislocation, the early canals wOlild have been palticularlysusceptible to destlUction by nooding.

Sometime betweenAD 600 and 700, Hohokalll uTiga­tion engineers designed the first large canals, capable oftransporting large quantities of water onto the upper, orsecond, terrace of the Salt River. By the early Colonialperiod (AD 700 to 900), large integrated callal systemswere 'established on both the. north and south sides of theriver. These Callais were often monwnental in theu' sizea11d scope. Many of the canals were over 12 miles Ullength, lvith the largest recorded Hohokam canal extend­ulg for 20 miles (32 km). 1\vo large prehistoric Callais arestill preserved Ul Park of the Four Waters, located in thesouthern portio!! of the Pueblo Grallde Musewn andCultural Park. The Callais measure 26 and 18 meters inlvidth and approximately 6.1 meters Ul depth. CanalSystem 2, the large system that heads on the Salt River atPueblo Grande, was probably capable of irrigatulg over10,000 acres of land.

Canal Engineering and Operation

Recent research,largely conducted Ul the corridorsof the expanding freeway system, is providblg new infor­mation concerniIlg the engineering of Hohokam Cal1al sys­tems. The Hohokam elJgineers were keenly aware of thelocal topography, the dips and slopes, draulages a11d soils.They developed a sophisticated knowledge of the now ofwater through chaiUlels and developed aseries of tech­niques for delivering water to the surface of the fields.Each teclmique was appropliate for a specific topographic

settlllg such as steep slopes and nat river ten·aces. TheCal1al systems were designed lvith respect to the needsand characteristics of the enviJ·omllent.

The canal systems contained aseries of physicalelements. Where the canal met the river it is likely that aweir would be constlUcted. Aweu' is a dam that reachesinto, but does not completely cross, the river. It raises thelevel of the water III the river and clirects it lllto the canal.Inside the canal, a headgate (a large water control gate),was probably constmcted to regulate the a1110unt of waterenteriJlg the Cal1al. The maill canals transported the wateraway from the liver toward the fields. Reseal'ch has shownthat the main canals are very large at theu' junction withthe river, but reduce in size as they progress toward theirtClTnlllUs. As the amount of water traveling through thecanal decreases tlu"Qugh discharge onto fields, evaporationand seepage, t.he size of the channel canying the wat.er isreduced. By reducing t.he chalUlel, the velocit.y of t.hewat.er (the speed it travels t.lu·ough the chamlel) remainedrelat.ively constant a11d between two critical thresholds:if the water t.raveled t.oo fast., {t eroded the sides of t.hecanal; if the water slowed down, particles of soil wouldsettle out of the water, causlllg the canal to quickly ·'silt.up;' and requiJ'e increased maintenance.

Distribution canals took water from t.he maill canalsyst.em and t.ransported it. t.o t.he fields. They were alsoused to manipulate the relat.ionship between t.he wat.erlevel in t.he canal and t.he grOlUld surface. Several types ofwat.er cont.rol feat.ures were used to operat.e clist.ributionsyst.ems. Diversion gat.es have been fOlUld at. the jlUlctionsof maill a11d distribution canals to regulat.e wat.er flow.Tapons or wat.er control gates were oft.en placed ulsidethe maill a11d distlibution canals. When closed, the taponwould cause tile water to back up and rise III elevat.ion,creat.ing a "head of water." Through the use of watercontrol features, the Hohokam were able to creat.e ahighly sophisticat.ed llTigation system.

Canal ConstluctionBuildblg t.he Hohokalll canals requiJ'ed a subst.aJltial

llwest.ment of human labor. The soil was removed byhalld, probably USlllg large wedge-shaped pieces of st.onecalled "stone hoes;' and wooden digging st.icks to loosenthe soil. The soil could t.hen be removed from t.he Callalusing large baskets. Variations on the sllnple "leveliJlgframe:' used III mailY prellldustrial agrarian societies,

~Pueblo Grande Museum and Cultural Park

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could have been employed to establish canal gradients. Ithas been suggested that water may have been carriedalong in the canal during construction to wet down or"loosen" the soil, However, such asystem would haverequired much more labor and time. The inundated canal, ~ ,would have to have been dammed and the water allowedto dissipate before the work could resume. Recent recon­structions ot prehistoric canals suggest that approximately800,000 cubic meters of soil may have been removed forthe construction of the main canals in Canal System 2dwing both the Colonial and Classic periods, and in excessof 400,000 cuBic meters dming the S,edentary period(AD 900-1100)

The alnOWlt of labor required to construct the canalsystem was partially dependent on the volume of waterflowing in the Salt Rivef. In b~th the late Colonial andClassic periods/the Hohokam exPerienced frequentflooding on the river. Thepood waters often damaged ordestroyed the canals, which we're then redesigned andrebuilt. It is difficult to estimate the actual time a,nd effOltrequired for the construction of the main canals. Manyfactors, including the·amount of soil a workercan removein a day, the number of homs worked in a day, the-numberof individuals wor!<in&, and the numbev of continuous orclispontinuous days/seasons over which the work is done,all affect estimates of time and labor expended. Given theability of a single worker to move 3m3 of soil per day, theconstruction of many canals would require in excess of25,000 person days. These data suggest that the construc­tion of some canals would have taken several years tocomplete.

Sociopolitical Organization ofInigation Societies

The construction, maintenance and operation of thecanal systems would have required a substantial and well­organized effort. Individuals from all of the villages along amain canal would wldoubtedly contribute to the initialconstruction and to the regular maintenance of the canal,weir and headgates. Each year, the amowlt of water allo­cated to each farmer was establishe~. Perpetual conflictsover water arise between individual farmers and villagesin irrigation societies even today. Thus, a strong leadershipmust have been necessalY to quickly resolve conflictswhich can threaten the cooperative ventmes required forthe continued operation of the large canal systems.

It is likely that the Hohokam canal systems werewuted into "irrigation commwlities;' sociopolitical wutscharacterized by a hierarchy with distinct leadership roles.Each in'igation commwlity would have its own leadershipto organize labor for main canal construction, maintenanceof the canals, headgates and weirs, the establislunent ofwater allocations and scheduling, and to resolve localconflicts. Smaller, more local groups of faImers couldorganize for the constiuction and maintenance of branchcanals and distribution canals. Unlike many oj the tradi­tional groups in the Southwest and northwestern Mexico,the Hohokam may have had a complex sociopoliticalstructure.

The Role ofPlatfonn MOlmds

Researchers have hypothesized that HohokaInplatform mounds were tied to the orgaIUzation and opera­tion of the canal systems. Large adrnil)istrative sites, con­tauling one or more platfOlm m01.!nds, occur at the headsof the major canal systems (ulcluding the sites of PuebloGrande, Mesa GraIlde, Plaza Tempe and Tres Pueblos).From this location, these sites controlled the flow of waterin the maUl canals and better organized the necessaIylabor of annual repairs to the weu's and headgates. OtherplatfOlm mounds are placed along the canals at regular,three-mile ultervals and may represent secondaIy centersthat controlled smaller telTitories along the canal system.

Some scholars suggest that the "elites" of Hohokamsociety lived on top of the platfonn mowlds. UnfOltunately,very few archaeological excavations of platform mowldshave been performed and reported. Amultiple volwnearchival report, bringing together the infOlmation obtainedfrom excavations of the Pueblo Grande mound from thelate 1920s to the present, is cmrently beulg prepared.This report, along with uUOlmation from the excavationsof several platform mowlds Ul the Tonto BasUl by ArizonaState Uluversity, \vill provide new data. New analysis ofthe cmrent infornlation on platfOlm mowlds is challengingearlier ulterpretations.

The platform mounds are contauled withiJllarger"compounds:' large reclaIlgular areas enclosed by a highwall (or "compound wall"). The architectme withiJl thecompounds includes a large public plaza Ul the easternsection of the mound and a series of rooms often locatedto the west of the mowld. High walls restricted accessfrom the public areas to the areas where the rooms were

~Pueblo Grande Museum and Cultural Park

Jeny B. Haward 1992

'I.:he Hohokam engineered large and sophisticatedcanal systems, creating a productive agricultural societythat spmwed many centwies. Their achievements in irri­gation engineering are among the most impressive andmost enduring ever constructed using preindustrial tech­nology. It is likely that a complex social and political struc­ture was developed to constmct and manage the canalsystem. The architectmal arrm1gement of the platfOlmmounds stresses the segregation and isolation of activities.This suggests aneed to control infOImation by limiting itsaccessil5ility and possibly a desire to maintain secrecy.Sites with platfOIm mounds appear to have selved as pos­sible ceremonial and/or administrative centers._ In anyevent, sites such as Pueblo Grande played crucial roles inthe construction, organization and operation of theHohokam canal systems. '

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located. Long passageways were often constmcted to pro­vide access from the public plaza to the rooms. The archi­tecturalliyout within the compounds does not suggest theusual residential patterns known to the Hohokam. Suchpatterns include an "interactive"series of houses or roomsarranged arow1d an open cowtyard where families wouldconduct daily activities. The rooms in the platform moundcomplexes tended to be isolated or separated from each ­other.1'his pattem appears to reflect the segregation ofactivities and a desire for secrecy, patterns often found inreligious architecture. ,I

This architectural arrangement suggests that theplatform mow1ds may have been more religious than sec­ular in their OIientation and function. While it does appearthat Hohokam society had leadership roles, the leadersmay not have lived in family muts residing on top of themounds. This perspective also suggests that HohokamreligiQ!1 may have played a prominent role in the organi­zation of the canal systems and the society.

Suggested Reading

Summary \

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Ackerly, Neal 1'1., Jerry B. Howard and Randall H. McGuire198? La Ciudad Canals: AStudy ofHolwkam

hTigation Systew; at the Cammunity Level.AJizona State University Anthropological FieldStudies, No.1? Tempe.

Breternitz, Cory D. (editor)19?1 Prehistoric Il1'igation in Arizona:

Symposium 1988. Soil Systems Publications inArchaeology No.1'?, Phoenix. '. • /

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Hawy, Emil IV.19?8 The Hohokam: Desmt Fanners and

Craftsmen. The University ofAJizona Press,Tucson.

Howard, Jerry B. and Gary Huckleberry1991 The Opemtion a.nd Evolution ofan h1'igation

System: The East Papago Canal Study. SoilSystems Publications in AJ'chaeology No. 18,Phoenix.

Masse, Bruce1981 PrehistOlic Inigation Systems in the Salt·River

Valley, AJizona. Science 214(23):408·415

Midvale, Frank1968 Prehistoric Irrigation in the Salt River Valley,

AJizona The Kiva 34:28·32.

Ttuney, Omar J

1929 Prehisf.o1;it; Irrigation in Arizona. AJizonaHistorical Review 2(5). Phoenix

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