Is Coronado actually an island?
Not quite. Geologists call it a tied island: it was surrounded by water thousands of years ago, then sand drifting north from the Tijuana River built the Silver Strand and reconnected it to the mainland.
- Geology
- Tied island
- Spanish Bight
- Filled 1944
- Population
- 20,192
Linked by a tombolo
Joined North Island
2020 census
The short version
- Between about 14,000 and 7,000 years ago, rising seas surrounded Coronado and made it a true island.
- The Silver Strand formed from sand carried north from the Tijuana River delta, tying it back to the mainland — a land-tied island connected by a tombolo.
- Coronado and North Island were separated by a shallow inlet, the Spanish Bight, until the Navy filled it by July 1944.
- Glenn Curtiss started a flying school on North Island in 1911; it became Naval Air Station North Island.
- The City of Coronado incorporated on December 11, 1890 and had 20,192 residents in the 2020 census.
Everyone calls it Coronado Island, and you can drive there without crossing the bridge — down the Silver Strand from Imperial Beach. Both things are true because Coronado is what geologists call a land-tied island: an island joined to the mainland by a sandbar, known as a tombolo.
How Coronado stopped being an island
Coronado Times (SDSU geologist Pat Abbott); Wikipedia, Coronado, California.
The Silver Strand is the tie
SDSU geologist Pat Abbott has explained that the Strand was built by longshore drift: waves hitting the coast at an angle push sand north, grain by grain, from the Tijuana River delta. Over thousands of years that ribbon of sand grew until it reached Coronado. Residents historically saw it flood at high tide, which is a reminder of how thin it is.
There used to be two islands
Coronado was also separated from North Island by a shallow inlet called the Spanish Bight. The Navy filled it in by July 1944 while expanding the air station, which is why today's map shows a single landmass with Naval Air Station North Island across its northern half.
Three ways to describe Coronado
| Island | Peninsula | Tied island | |
|---|---|---|---|
| Surrounded by water? | Yes | No | Almost — except a sandbar |
| Fits Coronado? | Only before the Strand formed | Loosely | Yes — the geologists' term |
| Example | Catalina | Point Loma | Coronado |
1890
City incorporated
20,192
Residents (2020)
~7.9 sq mi
Land area
KEEP READING
SOURCES
Everything above traces back to one of these. Follow them — if one has changed and we haven't, that's our mistake, not yours.
Coronado Times · July 27, 2017
Geologists' definition of a tied island; formation timeline from SDSU's Pat Abbott
- BackgroundCoronado, California
Wikipedia · Checked October 3, 2026
Spanish Bight filled by July 1944, incorporation date, 2020 population, land area
- PrimaryCoronado and the Navy
Coronado Historical Association · Checked October 3, 2026
North Island's naval aviation history