Two years after Major Riley's escort occurred an event of great consequence in the history of the Santa Fé trail. Josiah Gregg, impelled by ill health to seek a change of climate, made his first trip to Santa Fé in 1831. As an individual trader Gregg would call for no more comment than would any one who crossed the plains eight times in a single decade. But Gregg was no mere frontier merchant. He was watching and thinking during his entire career, examining into the details of Mexican life and history and tabulating the figures of the traffic. When he finally retired from the plains life which he had come to love so well, he produced, in two small volumes, the great classic of the trade: "The Commerce of the Prairies, or the Journal of a Santa Fé Trader." It is still possible to check up details and add small bits of fact to supplement the history and description of this commerce given by Gregg, but his book remains, and is likely to remain, the fullest and best source of information. Gregg had power of scientific observation and historical imagination, which, added to unusual literary ability, produced a masterpiece.
The Santa Fé trade, begun in 1822, continued with moderate growth until 1843. This was its period of pioneer development. After the Mexican War the commerce grew to a vastly larger size, reaching its greatest volume in the sixties, just before the construction of the Pacific railways. But in its later years it was a matter of greater routine and less general interest than in those years of commencement during which it was educating the United States to a more complete knowledge of the southern portion of the American desert. Gregg gives a table in which he shows the approximate value of the trade for its first twenty-two years. To-day it seems strange that so trifling a commerce should have been national in its character and influence. In only one year, 1843, does he find that the eastern value of the goods sent to Santa Fé was above a quarter of a million dollars; in that year it reached $450,000, but in only two other years did it rise to the quarter million mark. In nine years it was under $100,000. The men involved were a mere handful. At the start nearly every one of the seventy men in the caravan was himself a proprietor. The total number increased more rapidly than the number of independent owners. Three hundred and fifty were the most employed in any one year. The twenty-six wagons of 1824 became two hundred and thirty in 1843, but only four times in the interval were there so many as a hundred.