Where mountains drop off into a desert, as these Central Asiatic ranges
do, their piedmont cities are confined to a narrow zone between
mountains and arid waste. Bordering two transit regions of scant
population and through travel, they become natural outfitting points,
centers of exchange rather than production. Where mountains drop off
into the sea and the piedmont therefore becomes a coastal belt, again it
borders two transit regions; but here the ports of the desert are
replaced by maritime ports, which command the world thoroughfare of the
ocean. They therefore tend to concentrate population and commerce
wherever a good harbor coincides with the outlet of a transmontane
route, as in Genoa and Bombay.

[Sidenote: Piedmonts as colonial or backwoods frontiers.]

Since mountains are inhospitable to every phase of the historical
movement, they long remain regions of retardation. Hence to their
bordering plains they sustain the relation of young undeveloped lands,
so that life in their piedmont belts tends to show for a long time all
the characteristics of a new colonial frontier. The rim of the Southern
Appalachians abundantly illustrates this principle even to-day. During
the westward expansion of the American people from 1830 to 1850, the
eastern rim of the Rocky Mountains was dotted with trading posts like
that of the Missouri Fur Company at the forks of the Missouri River,
Forts Laramie and Platte on the North Fork of the Platte, Vrain's Fort
and Fort Lancaster on the South Fork, Bent's Fort at the mountain exit
of the Arkansas River, and Barclay's in the high Mora Valley of the
upper Canadian. These posts gathered in the rich pelts which formed the
one product of this highland area susceptible of bearing the cost of
transportation to the far away Missouri River. Though they developed
into way-stations on the overland trails, when the movement of
population to California and Oregon in the forties and fifties made the
Rocky Mountains a typical highland transit region, yet they long
remained frontier posts.[1201] Later the abundant water supply of this
piedmont district, as compared with the arid plains below, and the
mineral wealth of the mountains concentrated here an agricultural and
industrial population.

In Sze Chuan province of western China, the piedmont of a vast highland
hinterland shows a similar development. Here the towns of Matang,
Sungpan, Kuan Hsien, and even the capital Chengtu, situated in the