There were earlier gold strikes (Georgia for example in the early nineteenth century) but the classic, pivotal event was the California Gold Rush of 1849 (giving us the famed '49ers). This was spawned by the discovery of extensive (i.e. widespread) deposits of surface and near-surface gold dust and nuggets across a wide zone of the western slope of the Sierra Nevada. Because the deposits were on or near the surface, virtually any idiot could go to the gold country and have a reasonable hope of making his (or sometimes her!) "pile." This was usually enough to dream of returning home and buying a farm. Many made a bit of money. Not as many returned as planned to do so initially. But basically, most of the money was made by the person selling the pick rather than the one wielding it.

The richest surface deposits were exhausted within two or three years, resulting a period of technological innovation. This included the use of hydraulic mining, which consisted of using high-pressure water to erode mountainsides and accelerate the process that had left bits of gold in streambeds over the millennia. This was quickly outlawed by downstream users of water since it created an environmental disaster.

The most important technological move involved underground exploration and exploitation of intense precious metal veins. Although the Empire Mine (and others) opened in the Gold Country by the mid 1850s, the most important event in this regard was the 1859 discovery of the Comstock Lode in what is now western Nevada. This gold and silver vein was thought to be about four miles long (it now appears to be much longer) and it yielded twenty-years of epic mining that produced phenomenal wealth and, more importantly, generated cutting edge technology for underground mining. The inventions first tested on the Comstock were exported internationally, but initially, they resulted in the exploration and settlement of the "Intermountain West." Much of the image of the classic western boomtown is a result of this process, which is responsible for everything from Deadwood to the prospecting of the area that unfolded in the Battle of the Little Big Horn in June 1876.

A final invention that was first seriously tested and developed on the Comstock, involved cyanide processing of silver and gold ore beginning at the turn of the century. All of these innovations allowed for the exploitation of more and more marginal ore bodies, which meant that mining districts could continue to be operational long after the richest deposit were exploited, keeping settlements alive far longer than would have been possible with earlier technologies.

I'm not sure what specifically you're after, but this should give you a start.