Geologic Timeline

A step back in time starting with the coming of the age of mammals…

Atop Sierra de Alamos at sunrise, Alamos, Sonora, Mexico. Photo by Anders Tomlinson.

Atop Sierra de Alamos, near Gringo Point, looking south at sunrise into Sinola.

So much of is about history. In that spirit let us peek at the region’s geologic history, stand earth time. The Sierra Madre Occidental and the Rocky Mountains began to form 90 to 30 million years ago along the west coast of North America. Ocean levels were much higher than today, back then there was no Florida. The age of mammals started 66.4 million years ago. Sierra de Alamos was beginning under great pressure deep in the earth along with what would become Aduana’s silver deposits.

Granite Outcroppings on Sierra de Alamos, Alamos, Sonora, Mexico.  Photo by Anders Tomlinson

Sierra de Alamos is granite, only recently has it emerged from the earth.

Northwest Mexico, including Alamos, was buried under thousands of feet of ash, cinder and lava flows. Volcanic eruptions began 25 million years ago and continued another 12 million years, give or take a day or two. The Sea of Cortez began to form 12 to 3 million years ago as the Basin and Range block building was underway. Sierra de Alamos was still underneath a layer of all things volcanic. Over time erosion cut into ash flow plateaus creating landmarks like Barrancas del Cobre, Copper Canyon, whose materials were washed away and deposited near Sierra de Alamos. The rising mountain was still cover by blankets of earth.

View from atop Mt. al;amos looking south west, Alamos, Sonora, Mexico.  Photo by anders Tomlinson.

Atop the mountain looking southwest towards farmland and the Sea of Cortez.

As time marched on climate changed. The region began to cool 15 to 30 million years ago. Two to four million years ago it was warming up and raining. Most of the past two million years has been an ice age with 15 to 20 glacial periods. And now the planet is warming again. From a distant gallery it may look as if earth’s climate ebbs and flows like clockwork as the solar winds race past our blue planet, a molten rock with the thinest of crust and atmosphere.

Atop Mt. Alamos looking north at Alamos, Sonora, Mexico.  Photo by Anders Tomlinson.

Spring time on the mountain looking north with Alamos waking up below.

Today, Sierra de Alamos rises thousands of feet above its surroundings. And many have visited Alamos to research the region’s geology, flora and fauna. Josephine Scripps was asked by the San Diego Natural History Museum in the 1940’s to lead a group of six young men, none who spoke spanish, on a natural science expedition to Alamos. They were to bring back a rare mountain sheep’s skeleton and hide. Josphine, 1910 -1992, was the granddaughter of Edward Scripps, founder of the Scripps – Howard newspaper chain. Her life-long pursuit of collecting mineral specimens from across the planet began on that trip to Alamos.

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