Frequently Asked Questions:

Q. How old are rocks in the Franklin Mountains?
A. Some really, really old rocks are in the Franklin Mountains—some more than 1 billion (1,000,000,000) years old! These rocks are so old that they are from a time in Earth’s history when hardly anything was alive in the oceans, and what life existed, such as small soft-bodied animals with no shells or bones, is rarely preserved as fossils. You can see these old rocks in the road cuts along Trans-Mountain Road and in the generally dark-colored hills nearby; you can also see them many places along the lower slopes of the Franklins. Geologists call rocks this old “Precambrian.”

The youngest rocks in the Franklins are Permian age, or about 270 million (270,000,000) years old. Permian-age rocks are present in the Tom Mays unit of Franklin Mountains State Park.

Q. How big are they?
A. The Franklins are a long, skinny mountain range, which is typical of mountains in extensional areas such as the Rio Grande Rift. The highest peak in the Franklin Mountains is North Franklin Mountain. The top of North Franklin Mountain has an elevation of 7,192 feet (elevation means how high it is above sea level). A typical elevation at the base of the mountains is about 4,150 feet, which is also about the lowest elevation within Franklin Mountains Park. The “relief” of mountains, the difference between the highest elevations and the base of the mountains, is about 3,000 feet.