California Coastal Dunes Shrink 60% Since 1800s

A USGS-led study finds the state has lost roughly three-fifths of its historical coastal dune area over 165 years.

Updated on Nov. 10, 2026 in Geography

Screen-print poster illustration of a single pale grass-covered dune ridge beside a rust concrete edge, with teal sea and cream sky beyond. — A USGS-led study finds California has lost roughly 60% of its coastal dunes since the mid-1800s, mostly to structures built directly on dune fields. AI Illustration. Upload story photo >

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A USGS-led study found California has lost 60% of its coastal dunes since the mid-1800s, a reduction of 442 square kilometers. Current dunes extend along 352 km, or 22%, of the state's 1,625-km coastline and cover almost 300 square kilometers.

Why it matters

Decades of urban development, erosion and land-use change have left the remaining dune ecosystems smaller and more fragmented than they were historically. Fragmentation can make it harder for dune-dependent plants and animals to persist, move between habitats and adapt to changing conditions.

The figures come from comparing historical maps with modern imagery and LiDAR, showing a 60% loss of dune area since the mid-1800s. The study does not address how remaining dune populations will fare under continued fragmentation.

The players

U.S. Geological Survey (USGS)

The USGS is the science agency of the U.S. Department of the Interior that led the study on California's coastal dune loss.

The details

Researchers compared historical maps from the mid-19th century with modern aerial imagery and LiDAR data, using a machine-learning tool to estimate former dune extent. Most of the lost coverage came from structures built directly on top of dune fields, including much of San Francisco.

The baseline for comparison is the mid-1800s, when historical dune extent was mapped.
Roughly three-fifths of historical dune area has been lost over the past 165 years.

Historical Context

The loss traces back to 19th-century development that built directly over dune fields, as seen in San Francisco, where much of the city now sits on former dunes. The study places that local pattern within a statewide decline of roughly three-fifths of historical dune area since the mid-1800s.

Coastal dunes are habitat for plants and animals that depend on them, and fragmentation can limit their ability to move and adapt. Residents and planners in coastal areas may see this shift in local land use and habitat over time.

The takeaway

Coastal dune loss shows how development built directly on natural landforms can reduce habitat over generations. Understanding where dunes once stood can help inform decisions about what remains.