Sierra Rica complex, comprising the San Carlos and Santana
Calderas.
West Texas was the site of extensive volcanic activity during
the Eocene (about 28 million years ago).
This activity extended across the border into northern Mexico
where the Sierra Rica complex is located.
However, many of the tuffs extended into the United States
and are well exposed along the Rio Grande and in Big Bend Ranch State Park
where they are preserved.
The following airmail stamp was issued in 1999.
The photographer, Bruce Dale of Arlington Virginia,
kindly located the site of the photograph as being about 5
miles upriver from the town of Lajitas.
The following map shows the distribution of the calderas within
this Eocene time-frame.
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of the US and Canada
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