Farmers and miners of the intermountain West shared an interest in having a bi-metal precious metal standard as opposed to one exclusively backed by gold. After the "Crime of '73," referring to the congressional Mint Act of 1873 and the demonetization of silver, the value of the precious metal was vulnerable and declining. The push for "Gold standard" politicians was to restrict the minting of silver coinage in preference for those of gold: silver was reserved for use in lower-valued coins and there was an effort to also restrict it for only trade dollars (for use in foreign markets). This was not entirely successful as the federal government continued to mint silver dollars for domestic use. That said, the federal government, one of the main markets for Western silver, reduced the amount of the precious metal it purchased.

All of this represented a direct threat to the Western mining economies. The 1885 inauguration of the democrat, President Groover Cleveland (1837-1908), heighten the urgency felt by Western silver mine owners: Cleveland was wedded to the gold standard, free of reliance on silver, earning him the nickname, "Goldbug" Cleveland. The perceived threat was enhanced when Cleveland suspended production at Carson City's U.S. Mint in 1885, which was an important market place for Comstock silver.

The goal of the 1873 act was to restrict the money supply, to control the national economy. The value of silver fell, contributing a depression in the Nevada and other Western economies, felt severely by the 1880s. Restricted access to currency also hurt Midwestern farmers who needed to borrow money for agriculture, which is vulnerable to extremes in productivity and value. Bolstering the value of silver became a populist call for reordering the structure of wealth in the nation. Throughout the rest of the nineteenth century and into the next, a return to "bimetallism" with currency linked to a set value for gold and silver, became central to populist politics. Silver advocates and agrarian populists hoped to "remonetize" silver, with the goal of seeing U.S. coins minted at a ratio of sixteen to one, silver to gold.

Edit: The goal of bi-metalism is behind the fact that in the populist novel of L. Frank Baum (1856-1919), The Wonderful Wizard of Oz (1900), while Dorothy travels on the "yellow brick" (i.e. gold) road when going to the Emerald City (i.e. Washington, D.C.), she wears silver shoes. In the film, the shoes were turned to a meaningless ruby color, which was better suited to the vivid colors of a film in 1939.

Sources: Allen Weinstein, Prelude to Populism: Origins of the Silver Issue, 1867-1878 (New Haven: Yale University Press, 1970); Allen Weinstein, "Was there a 'Crime of 1873'?: The Case of the Demonetized Dollar," Journal of American History, 54 (September 1967) 307-27; Mary Ellen Glass, Silver and Politics in Nevada 1892-1902 (Reno: University of Nevada Press, 1969).

Free silver wasn't the idea that the government should start minting gold and silver-it was the idea that the government mints should be required to allow the free exchange of silver bullion (or metal) directly into currency.

Suppose I was, say, a private miner and I had found a small supply of gold and silver metal. Under US monetary policy at the time, I could exchange my gold directly for gold coins. Essentially, let's say I had found 1 lb of gold, and that each gold dollar contained 1 ounce of gold. Since there are 16 ounces to a lb, I could exchange my pound of gold at a mint directly for 16 gold dollars. This was not the case for silver, despite silver also being a precious metal. Free-silver proponents wanted this to be true for silver.

The problem was that the market value of the price of silver in silver coins (nickels, dimes, etc.) was less than the face value of the coin. So if you allowed for free-silver, you would have a situation where I took my pound of silver and exchanged it for silver coins based off of the metal content, even though the amount of silver in my dime may be worth only 5 cents. This would be a powerful inflationary force, as people would be strongly encouraged to exchange gold metal for silver metal and use it to get coins that were worth more than the metal they were minted with.

Obviously, the rich, who benefited from low inflation, were strongly against this movement. People with large amounts of wealth stand the most to lose from inflation as over time the value of their assets will go down (from a real value perspective). On the other hand, the poor, especially people who were in debt, would gain, as the real value of their debt would go down over time. Thus the main supporters of free-silver were poor farmers and debtors, against wealthy capitalists and the banks who were against it.