The San Andreas Fault extends down roughly 10 miles (about 16 km) into the Earth , and in many places is described as reaching depths of “at least” that much.

Quick Scoop

  • Geologists estimate the San Andreas Fault system reaches at least ~10 miles (16 km) deep , based on seismic and structural studies.
  • Some popular and secondary sources suggest parts of the fault might extend closer to 20 miles (32 km) , but this deeper figure is not well confirmed in the scientific literature.
  • Depth is not uniform : the fault is a broad zone of broken rock that can be a few hundred feet to about a mile wide near the surface, narrowing with depth into a more discrete fracture.

How Scientists Know The Depth

  • Agencies like the USGS describe the San Andreas system as more than 800 miles long and extending to depths of at least 10 miles, based on earthquake locations and geophysical imaging.
  • A deep drilling project near Parkfield, California (the San Andreas Fault Observatory at Depth) reached over 2 km into the fault zone to study its properties directly, but even that is only a small fraction of its full depth.

Why Depth Varies By Location

  • The San Andreas is not a single clean crack; it is a complex network of fault strands whose geometry changes along its length and with depth.
  • In some segments the seismically active portion of the fault tapers or changes dip between about 6–9 km depth, reflecting different rock behavior at shallow versus deeper levels in the crust.

Forum & “Trending Topic” Angle

  • Online discussions and travel pieces often cite the fault as “about 10 miles deep” and highlight that scientists cannot yet map its full three‑dimensional structure perfectly, which keeps some aspects “mysterious.”
  • Viral posts that claim dramatic crevices “32 km deep” are usually misattributed photos or refer to other features, not an actual open trench down the full depth of the San Andreas Fault.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.