His horse was stripped of all unnecessary weight, too.

He wore a little wafer of a racing-saddle, and no visible blanket.
He wore light shoes, or none at all.

The little flat mail-pockets strapped under the rider's thighs would each hold about the bulk of a child's primer.

They held many and many an important business chapter and newspaper letter, but these were written on paper as airy and thin as gold-leaf, nearly, and thus bulk and weight were economized.

The stage-coach traveled about a hundred to a hundred and twenty-five miles a day (twenty-four hours), the pony-rider about two hundred and fifty.
There were about eighty pony-riders in the saddle all the time, night and day, stretching in a long, scattering procession from Missouri to California, forty flying eastward, and forty toward the west, and among them making four hundred gallant horses earn a stirring livelihood and see a deal of scenery every single day in the year.
We had had a consuming desire, from the beginning, to see a pony-rider, but somehow or other all that passed us and all that met us managed to streak by in the night, and so we heard only a whiz and a hail, and the swift phantom of the desert was gone before we could get our heads out of the windows.