Images

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the border of Texas and Mexico.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the border of Texas and Mexico. This view is of the cliffs of Diablo East.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the Texas and Mexico border. It is fed by the Rio Grande, Devils River, and the Pecos River, among others.

A series of flowstone draperies in the Caverns of Sonora.

A pool in the Caverns of Sonora. This cave, like many others, was formed by water combining with carbon dioxide to create a weak carbonic acid. This acid then dissolved the limestone to carve out chambers.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the Texas and Mexico border. It is fed by the Rio Grande, Devils River, and the Pecos River, among others.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the Texas and Mexico border. It is fed by the Rio Grande, Devils River, and the Pecos River, among others.

The Caverns of Sonora have numerous types of speleothems, or cave formations. In this image, stalactites can be seen hanging from the ceiling; stalagmites can be seen rising from the floor; and all along the walls are small formations known as "cave popcorn." The central focus of the image are several columns, which occur when stalactites and stalagmites fuse.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the Texas and Mexico border. It is fed by the Rio Grande, Devils River, and the Pecos River, among others.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the Texas and Mexico border. It is fed by the Rio Grande, Devils River, and the Pecos River, among others.

A series of stalagmites, a form of dripstone that grows from the floor of a cave, in the Caverns of Sonora.

A prominent cave column in the Caverns of Sonora. Cave columns occur when stalactites and stalagmites fuse together. This column then grew a series of cave formations, or speleothems, known as "cave popcorn."

A series of bulbous cave formations known as "cave popcorn." The geode-like formation in the center developed, because, at one point, this portion was submerged in water. Water was moving on the surface, creating the smooth appearance, while the opening allowed water to pool.

Cave formations depend on water flowing through the limestone that makes up the cave walls. As the water passes through, it dissolves the limestone. Then, the calcium recombines with carbon dioxide in the water to create calcium carbonate.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the border of Texas and Mexico. This view is of the cliffs of Diablo East.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the border of Texas and Mexico. This view is of the cliffs of Diablo East.

Amistad National Recreation Area includes the Amistad Reservoir, a man-made lake along the Texas and Mexico border. It is fed by the Rio Grande, Devils River, and the Pecos River, among others.

A panorama of speleothems, or cave formations, in the Caverns of Sonora.

The Caverns of Sonora have numerous types of speleothems, or cave formations. In this image, stalactites can be seen hanging from the ceiling; stalagmites can be seen rising from the floor; and all along the walls are small formations known as "cave popcorn."

Sheets of cave popcorn in the Caverns of Sonora.

A speleothem known as a "whale's tail." The fan shape comes from the calcium-carbonate-bearing water being forced through small openings and leaving the calcium carbonate behind in the distinctive fan shape.