Yes, Mother Nature did make the "floor" that you see here. About
100,000 years ago a 400 foot thick molten mass of lava cooled and
shrunk, breaking into long vertical shafts, each multisided like a
pencil, and about a foot and a half in diameter, creating a rock
formation known as "columnar basalt." Later a glacier
ground its way across the mass, leaving a surface flat as a floor
with the long thin parallel scrape marks across it that you see.
is located about 200 miles east of San Francisco.
The postpile is cool enough that you might just want to look around
it a bit. If you'd like to see more, check out our
The floor-like appearance of the formation begs to be sat upon.
The above photo was taken during a visit to the postpile on June 17, 1994.
On a subsequent visit on September 19, 1997, my friend Louis
caught me with his camera (below), sitting on the postpile again!