Why Do Trees Grow in Desert Washes That Look Completely Dry?

Look across a dry desert slope and you may see a line of larger plants following a pale channel. There may be no visible stream, no pond and no obvious source of water.

The trees are part of the explanation. They draw attention to the places where water moves, collects and sometimes remains after the surface looks dry again.

A wash collects water from more than one patch of sky

A desert wash is a drainage channel that carries runoff intermittently. It gathers water from a surrounding catchment, so the plants along it may benefit from rain falling across a much larger area than the ground directly beneath them. Water, sediment, nutrients and seeds can all move along that channel. [1]

This helps explain why a line of trees can trace an otherwise dry valley floor. The visible channel is part of a collection system. Its importance is not measured only by how often a visitor sees flowing water.

A wash near the Salton Sea described by the Arizona-Sonora Desert Museum illustrates that contrast: trees occupy a drainage that carries water infrequently. The specific frequency varies from wash to wash and year to year. [2]

Follow a pulse of water

Meet the plants that help draw the channel

Depending on the wash and its conditions, the tree and shrub community may include palo verde, smoke tree, mesquite, ironwood, desert willow or catclaw acacia. These plants do not all use water identically, and every wash will not contain every species. [5]

Palo verde offers an easy starting point for close observation. Its green branches and small leaves give it a different appearance from the broad, dense canopy many people expect when they hear “tree.” Photograph its outline first, then the branch and leaf details.

A dry wash is not automatically an underground river

It is tempting to imagine a permanent stream just below any tree-lined channel. The reality is more varied. Some plants use water stored in soil after intermittent runoff; in other settings, deeper or more persistent moisture matters. Plant roots and water availability depend on species and local conditions. [4]

A spring-fed palm oasis is a different case. At the Coachella Valley Preserve, faults help groundwater reach the surface. That documented water source should not be assumed beneath an unrelated wash simply because trees are present. [6]

The useful question is “How does water reach this plant?” A photograph can reveal a pattern to investigate, but it cannot answer that subsurface question by itself.

Read the pattern on your next walk

From an established route, look across the landscape before concentrating on a single tree. Do the larger plants form a line? Is that line lower than the surrounding ground? Can you see a tributary drainage entering it, or deposits of gravel and sand?

For a useful photograph, include the wash, its plants and the slopes that drain toward it. A close-up of foliage identifies the subject; a wider composition helps explain why it is growing there. The La Quinta Cove trails and Randall Henderson Loop offer local landscapes to study in suitable weather.

When you return in dry weather, the channel may look quiet again. The line of plants is a reminder that an intermittent event can leave a lasting pattern in the landscape.

For the broader drainage story, including the valley’s flood channels, continue with Where Does the Water Go When It Rains? This plant-focused guide and that drainage guide explore the same landscape from different starting points.