Rocks from the Tertiary or younger

In the map are shown the rock outcrops dating from the Tertiary:

From the Tertiary:

These outcrops correspond mainly to lava flows (most of them rhyolites), as well as fluvial or lake deposits of volcanic ashes. These latest rocks are, for instance, the cliffs on Elias or Campillo streets, which geologically have been named the Nogales Formation.

The Nogales Formation has been dated from around 13 million years ago, and corresponds to spillages of volcanic ashes mixed with other types of rocks.

These rocks were deposited when, not only in today's Nogales but all of the West Coast of Sonora was under a period of intense and explosive vulcanism.

It was precisely then when the Sierra Madre Occidental was born as an enormous layer of rhyolitic lava flows which covered all of Central Mexico.