University of Arizona

Sense of Place

Geos. 195D

Tucson Desert Washes

Illustration by Dennis Caldwell,
Map shared courtesy of Watershed Management Group

Tucson washes are mostly dry, except when they flood.

The Rillito in moderate flood,
with lots of muddy water.

Click to see a short video of the January, 2015,
flooding of the Rillito.

Click to see a short 2022 newsclip of past flooding of Tucson.
  • The Rillito experienced a peak flood during late July, 2006. Click here to see the USGS report on it, and here to see a video of it. Very impressive!
  • '83 flood-control work helps limit damage: This AZ Daily Star article says the side wall cementing of our washes helped get us through the July '06 flooding.
  • Marana floods: Then again, the downstream community of Marana took a hit in the July '06 flood.

The Rillito (Río-ito, little river)

The Rillito-Pantano watershed is 588,800 acres (920 square miles) in area, starting in Santa Cruz County and flowing north-northwest. The Rillito runs along the north side of Tucson and drains into the Santa Cruz River just south of Orange Grove Rd.

Pantano Wash - Rillito River Watershed, Arizona: Rapid Watershed Assessment
Looking south (pano) and down (aerial) at the Rillito between Craycroft and Swan.
Shallow but wide, loaded with burrobush.

Modern Settlement Along the Banks of Tucson Washes

A sense of place conundrum: Should houses and business be built in or near Tucson's washes?

Settlements Along the Banks of Tucson Washes

People have been living along the banks of the Rillito and the Santa Cruz for millennia. For example, here's a map of archaeological sites along the Santa Cruz.
March 23, 2014: Arizona Daily Star.

Bank-full Discharge Measurement

It's possible to measure the maximum bank-full discharge (volume of water per unit time) rate of washes, even when they're dry.

First, stream cross-sectional area.

Then, slope using a topo map.

Then, back of the envelope.


Dendrochronology, the study of tree rings, can be applied to riparian trees to date past floods.

2011: Coring a tree.
Photo — Jason Eckelbarger

2011: A tree core. Photo — Rachel Feuerbach

Cemented Banks

The banks of the Rillito have been cemented in, aka, re-inforced (see map below), which protected many "streamside" areas during the July, 2006, flooding. Will the cement hold out forever?

Engineering cross-section

2009: Photo — Paul Sheppard

2007: Photo — Jayme Kelter

2007: Photo — Jayme Kelter

2022 repeat photo — Gary Huckleberry

2014: Seeking shade, Pima Wash.
Photo — Gary Huckleberry

Map of bank reinforcement of Tucson washes.

Desert Wash Humor

  • Click here to see a K. Rat comic on cleaning out Tucson washes of all vegetation.
  • Right: watch out for the cyclists on this trip!

2018: Fitzsimmons, AZDS

The Rillito Freeway

Rillito Freeway: A plan has been floated to build a crosstown freeway on the Rillito, and continuing on the Pantano. Is this a good idea? As usual, pros and cons?

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