Most notable among the ante-bellum pioneers in California was John A. Sutter, whose establishment on the Sacramento had been a centre of the new life. Upon a large grant from the Mexican government he had erected his adobe buildings in the usual semi-fortified style that distinguished the isolated ranch. He was ready for trade, or agriculture, or war if need be, possessing within his own domain equipment for the ordinary simple manufactures and supplies. As his ranch prospered, and as Americans increased in San Francisco and on the Sacramento, the prospects of Sutter steadily improved. In 1847 he made ready to reap an additional share of profit from the boom by building a sawmill on his estate. Among his men there had been for some months a shiftless jack-of-all-trades, James W. Marshall, who had been chiefly carpenter while in Sutter's employ. In the summer of 1847 Marshall was sent out to find a place where timber and water-power should be near enough together to make a profitable mill site. He found his spot on the south bank of the American, which is a tributary of the Sacramento, some forty-five miles northeast of Sacramento.
In the autumn of the year Sutter and Marshall came to their agreement by which the former was to furnish all supplies and the latter was to build the mill and operate it on shares. Construction was begun before the year ended, and was substantially completed in January, 1848. Experience showed the amateur constructor that his mill-race was too shallow. To remedy this he started the practice of turning the river into it by night to wash out earth and deepen the channel. Here it was that after one of these flushings, toward the end of January, he picked up glittering flakes which looked to him like gold.
With his first find, Marshall hurried off to Sutter, at the ranch. Together they tested the flakes in the apothecary's shop, proving the reality of the discovery before returning to the mill to prospect more fully.
For Sutter the discovery was a calamity. None could tell how large the field might be, but he saw clearly that once the news of the find got abroad, the whole population would rush madly to the diggings. His ranch, the mill, and a new mill which was under way, all needed labor. But none would work for hire with free gold to be had for the taking. The discoverers agreed to keep their secret for six weeks, but the news leaked out, carried off all Sutter's hands in a few days, and reached even to San Francisco in the form of rumor before February was over. A new force had appeared to change the balance of the West and to excite the whole United States.
The rush to the gold fields falls naturally into two parts: the earlier including the population of California, near enough to hear of the find and get to the diggings in 1848. The later came from all the world, but could not start until the news had percolated by devious and tedious courses to centres of population thousands of miles away. The movement within California started in March and April.
Further prospecting showed that over large areas around the American and Sacramento rivers free gold could be obtained by the simple processes of placer mining. A wooden cradle operated by six or eight men was the most profitable tool, but a tin dishpan would do in an emergency. San Francisco was sceptical when the rumor reached it, and was not excited even by the first of April, but as nuggets and bags of dust appeared in quantity, the doubters turned to enthusiasts. Farms were abandoned, town houses were deserted, stores were closed, while every able-bodied man tramped off to the north to try his luck. The city which had flourished and expanded since the beginning of 1847 became an empty shell before May was over. Its newspaper is mute witness of the desertion, lapsing into silence for a month after May 29th because its hands had disappeared. Farther south in California the news spread as spring advanced, turning by June nearly every face toward Sacramento.
The public authorities took cognizance of the find during the summer. It was forced upon them by the wholesale desertions of troops who could not stand the strain. Both Consul Larkin and Governor Mason, who represented the sovereignty of the United States, visited the scenes in person and described the situation in their official letters home. The former got his news off to the Secretary of State by the 1st of June; the latter wrote on August 17; together they became the authoritative messengers that confirmed the rumors to the world, when Polk published some of their documents in his message to Congress in December, 1848. The rumors had reached the East as early as September, but now, writes Bancroft, "delirium seized upon the community."
How to get to California became a great popular question in the winter of 1848–1849. The public mind was well prepared for long migrations through the news of Pacific pioneers which had filled the journals for at least six years. Route, time, method, and cost were all to be considered. Migration, of a sort, began at once.
Land and water offered a choice of ways to California. The former route was now closed for the winter and could not be used until spring should produce her crop of necessary pasturage. But the impetuous and the well-to-do could start immediately by sea. All along the seaboard enterprising ship-owners announced sailings for California, by the Horn or by the shorter Isthmian route. Retired hulks were called again into commission for the purpose. Fares were extortionate, but many were willing to pay for speed. Before the discovery, Congress had arranged for a postal service, via Panama, and the Pacific Mail Steamship Company had been organized to work the contracts. The California had left New York in the fall of 1848 to run on the western end of the route. It had sailed without passengers, but, meeting the news of gold on the South American coast, had begun to load up at Latin ports. When it reached Panama, a crowd of clamorous emigrants, many times beyond its capacity, awaited its coming and quarrelled over its accommodations. On February 28, 1849, it reached San Francisco at last, starting the influx from the world at large.
The water route was too costly for most of the gold-seekers, who were forced to wait for spring, when the trails would be open. Various routes then guided them, through Mexico and Texas, but most of all they crowded once more the great Platte trail. Oregon migration and the Mormon flight had familiarized this route to all the world. For its first stages it was "already broad and well beaten as any turnpike in our country."