Red Sandstone

Red Sandstone is a solid block. It is found naturally at entrances of mesa caves, and can also be crafted from red sand. Unlike regular sandstone, it does not generate under piles of sand.

Chiseled Red Sandstone is a decorative form of red sandstone with a Wither carving on it.

Smooth Red Sandstone is a decorative form of red sandstone with a smoother texture.

Natural generation
Red Sandstone generates naturally at cave entrances in mesa biomes. The amount of Red Sandstone that generates is highly variable; some caves may generate a large amount of Red Sandstone, while others may generate just one block.

Trivia

 * The Chiseled Red Sandstone also has an "H" and a "C" on it, under the Wither. It is currently unknown what they represent
 * The idea of the Wither appearing on Chiseled Red Sandstone was suggested by Reddit user ULiopleurodon.
 * Jeb stated that "maybe one day" he might design a desert temple-like structure to generate in mesas, using Red Sandstone and its variants.