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Cars drive through deep floodwater on Melrose Avenue in Los Angeles during heavy rain, highlighting stormwater pooling in the Fairfax Basin. Cars drive through deep floodwater on Melrose Avenue in Los Angeles during heavy rain, highlighting stormwater pooling in the Fairfax Basin.

Why Parts of Los Angeles Flood During Heavy Rain: The Geology of the Fairfax Basin

Heavy rain repeatedly floods parts of Los Angeles because the Fairfax District sits inside a former marsh basin shaped by tectonic forces and historic creeks. Modern pavement may cover it, but the geology remains.
Cars drive through deep floodwater on Melrose Avenue in Los Angeles during heavy rain, highlighting stormwater pooling in the Fairfax Basin.

After another round of heavy, unpredictable rain moved through Los Angeles, the same frustration returned across Fairfax and Melrose:

Streets flooded.
Storefronts pooled.
Traffic crawled through standing water.

And the question always follows:

“Why does this keep happening here?”

The answer isn’t just storm drains.

It’s geology.


Fairfax Sits Inside a Structural Basin

The Fairfax District lies within the Los Angeles Basin, a massive structural depression formed by tectonic movement over millions of years.

This isn’t flat land.

It’s a bowl.

Cross-section diagram showing the Fairfax District located inside the Los Angeles Basin, a sediment-filled tectonic depression beneath present-day ground level.
Illustration of the Fairfax District within the Los Angeles Basin, a structural depression formed by tectonic movement and later filled with sediment.

Water naturally flows toward lower elevations, and parts of Fairfax, Melrose, and the Grove corridor sit in one of those subtle low zones.

When intense rainfall hits in short bursts — which recent storms have delivered — runoff from slightly higher surrounding neighborhoods funnels inward.

If rainfall intensity exceeds drainage capacity, even briefly, water accumulates.

That’s not failure.

That’s gravity.


It’s Only Been Paved for About 100 Years

Aerial photograph from 1922 showing the La Brea Tar Pits in the Miracle Mile area with early development encroaching into the Fairfax District.
An aerial view from 1922 shows the La Brea Tar Pits surrounded by open land, as early development began expanding into what would become the Fairfax District.
Image credit: Miracle Mile Residential Association.

Modern Los Angeles feels permanent.

It isn’t.

A century ago, Fairfax was open chaparral basin, seasonal marshland, and oil seep terrain.

In geological terms, that’s yesterday.

We replaced permeable soil with concrete.
We buried natural drainage paths.
We flattened wetlands that once absorbed rainfall.

Concrete doesn’t absorb water.

It redirects it.

And when you redirect water inside a bowl, it pools.


“La Cienega” Means The Marsh — And That Wasn’t an Accident

Look west.

An 1858 plat map of Rancho La Ciénega and Rancho La Tijera in Los Angeles, showing early land boundaries and natural landscape features.
An 1858 survey plat of Rancho La Ciénega and Rancho La Tijera shows how the area was documented long before urban development. The name “La Ciénega” — meaning marsh — reflected the landscape settlers encountered.
Image credit: lastreetnames.com.

La Cienega Boulevard translates to “the marsh” or “the swamp.”

Early settlers named it based on what they saw: shallow groundwater and saturated terrain.

We didn’t rename the land.

We just covered it.


The Buried Creeks Still Shape Today’s Flooding

Historic runoff maps show multiple drainage paths threading through Fairfax.

Map showing former and current creek paths in the Hollywood and Mid-Wilshire areas of Los Angeles, including runoff channels through Fairfax and Miracle Mile.
A map of former and current creek paths in Hollywood and Mid-Wilshire shows how historic waterways continue to shape modern drainage patterns through Fairfax and Miracle Mile.
Courtesy of lacreekfreak.wordpress.com.

Three visible stormwater channels either originate or converge in this area before continuing south toward Miracle Mile.

Historically, small creeks moved through:

  • The Fairfax corridor
  • La Brea
  • Hauser
  • Near Rimpau
  • Through what is now The Grove and LACMA

Many were paved over or routed underground as the city expanded.

But the topography didn’t change.

Water still attempts to follow those original routes.

When rainfall is light, you don’t notice.

When rainfall is intense, the basin reasserts itself.


Check out the interactive creek map: See former and current creek paths across Hollywood and Mid-Wilshire — including runoff lines that converge near Fairfax.

Open the Interactive Creek Map

Courtesy of lacreekfreak.wordpress.com


The Tar Pits Confirm the Basin

A worker sits near sandbags during mammoth sculpture restoration at the La Brea Tar Pits in Los Angeles, with the tar pond and museum grounds visible behind a fence.
A worker pauses during mammoth restoration at the La Brea Tar Pits in Los Angeles. The site remains one of the clearest geological reminders that Fairfax sits within a historic basin.
Photo by Victor Atomic Lerma for INYIM, March 12, 2019.

The La Brea Tar Pits exist because this area historically trapped sediment, groundwater, and organic material in a low-lying zone.

That’s basin behavior.

During heavy storms, groundwater pressure rises. You may even notice increased seepage or that faint petroleum scent after rain.

The system is ancient.

The asphalt is young.


Why Recent Storms Feel More Severe

Heavy rain blurs a car windshield in Los Angeles during a storm.
Heavy rain blurs visibility during a Los Angeles storm, as intense downpours overwhelm streets across the Fairfax Basin.
Photo by INYIM.

The issue isn’t just rainfall totals.

Recent storms have delivered:

  • Short-duration, high-intensity bursts
  • Harder-to-predict rainfall patterns
  • Higher hourly accumulation rates

Urban drainage systems are designed for thresholds.

When rainfall exceeds those thresholds, surface pooling happens — especially in former marsh basins with buried creeks.

So what looks like:

“Why is this neighborhood broken?”

Is often:

“Why does water still follow gravity?”


The Line Worth Remembering

Historic 1920 photograph of Wilshire Boulevard near Fairfax in Los Angeles, with a wide paved road, open fields, a large tree in the foreground, and early oil development visible in the distance.
Wilshire Boulevard near Fairfax in 1920, when the corridor remained largely undeveloped and surrounded by open land. Within a decade, the Miracle Mile would begin transforming the basin into a commercial hub.
Courtesy of the Historic Los Angeles Facebook group.

We paved a marsh about 100 years ago and expected it to forget what it was.

It hasn’t.

When heavy rain hits Los Angeles, the Fairfax Basin behaves exactly like a basin.

And the bowl still fills.


Sources & Archival Materials

Historic maps and archival images referenced in this story include materials courtesy of the Miracle Mile Residential Association, the Historic Los Angeles Facebook group, and lacreekfreak.wordpress.com, used for editorial commentary.


From Los Angeles to anywhere built on former marsh, creek beds, or basins, these stories are often written into the land long before pavement arrives.

In the comments below, tell us what you’re seeing where you are.

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