Why are they piled up in particular spots?
This was at one time an inland sea. The trees floated here, and were swept by whirlpools or strong currents into eddys where they became waterlogged and sank.
How long ago was that?
Men who have made a lifetime study of it, say it was from ten to forty million years ago.
What became of the sea that was here?
Gradual upheaval of the country, aided by earthquakes and volcanic action, raised this area and drained it. The Sierras were probably brought to their present height during these disturbances.
What kind of trees are they?
Mostly an extinct species of cone bearing tree. (Araucarioxylon Arizonicum.)
How big were these trees?
Some of them are now a hundred feet long, and six to eight feet in diameter. The Natural Bridge is one hundred and eleven feet long. The height of some of these trees while standing was doubtless two hundred feet or more.