San Diego – A Brief Geological History of Paradise

Although Planet Earth itself is 4.5 billion years old, the oldest rocks in San Diego are comparatively young at only 150 million years of age. This should not really come as a surprise, as the reader realizes all the fault lines and as a result earthquakes in the area. Being on the edge of the continent, tectonic plate movement has forced up much magma into our area thus our area is relatively young.

Let us now skip ahead, by millions of years, as much of the topology of the area has been formed in the last 2.5 million years. There are two main forces shaping the region.

* First, sea levels have changed by hundreds of feet over this time as glaciers came and went during the millennia. It was not that our area had glacier cover, but much water was trapped in the glaciers affecting sea levels. It is easy to recognize old sea floors in our area by looking at the flat areas.
* Secondly, the area around San Diego has been rising as a result of tectonic activity. In fact, west of I-5 near San Diego, land is rising at the rate of 18 inches each thousand years.

If we looked at San Diego a mere 100,000 years ago, much of it was underwater. Only the tops of Point Loma and Mount Soledad would have been visible. As a result of sea levels and tectonic forces, however, water was able to cut channels through the land resulting in the topology you see in the area today.


For more current happenings, here are a few points of interest:

* North Island and Coronado Island were once separate pieces of land. This is because a fault line runs exactly between them. The Navy has filled in the area, but it is still geologically active.
* Mission Bay, as you may expect, is fairly young at around 10,000 years, and was formed by the ocean wave action depositing sand.
* The “Silver Strand” is a natural phenomenon caused by ocean waves coming from the south, and depositing sand.


Of course San Diego’s history can fill volumes, but hopefully you will have a bit better idea of the area that many of us call home.