Red Sandstone

Red Sandstone is a sedimentary rock found naturally at entrances of mesa caves, and can also be crafted. Unlike yellow sandstone, it does not generate under the red sand ground, rather, orange stained clay does this job.

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.

Obtaining
Red sandstone can be mined using any pickaxe. If mined without a pickaxe, the block is lost.

Natural generation
Red sandstone generates naturally at most cave entrances in mesa biomes. The amount that generates is highly variable; some caves may generate a large amount of red sandstone, while others may generate just one block, or even none. Liquid pools will not generate red sandstone, resulting in floating red sand which will fall when updated.

Trivia

 * The idea of the wither appearing on chiseled red sandstone was suggested by Reddit user ULiopleurodon.