Your observation about the depiction of western towns - and the question about food sources - is very well placed. The West (particularly the arid West) has consistently been one of most urbanized regions of North America, and the towns are often is the least likely of locations with no obvious natural resources. Mineral resources are too often found in the most bleak of circumstances!

Various sources demonstrate that many people in these towns kept chickens, and sometimes they kept other animals used for food, but this was hardly sufficient to support a large community. In addition, a large community quickly exhausted natural food resources in the vicinity.

If we reach back further in time, we can see the California Gold Country following the rush of 1849, and it is easy to understand how the then-smaller communities survived: California has ample opportunities for agriculture and the style of mining was not conducive to large communities. Placer mining pursues extensive mineral resources that are pursued by small groups of people. While co-editing the the Grosh letters (published in 2012) written from 1849 to 1857, it was clear that small parties of gold miners pursued their retrieval of gold, but usually one or more of the small group went hunting daily. This was usually done by men who had a good reputation for hunting. They were compensated with an equal share of gold retrieved. With gold in hand, someone was regularly sent to the nearest town to buy other supplies. That model was easily developed and implemented with very little infrastructure.

A crisis occurred in the West in 1859 with the discoveries of various underground gold and silver deposits in the West, remotely located and often in places where no sensible person would settle for lack of food and water. These were "intensive" deposits - veins of mineral resources - that required large underground operations, a switch from the earlier placer mining days.

Establishing how to address this situation, Virginia City and the great Comstock Lode became the internationally accepted model on how to build and support a large mining community in a remote location (again, see my book, The Roar and the Silence: A History of Virginia City and the Comstock Lode (1998)). As was often the case, this sort of community required the importation of everything from food, lumber, clothing, tools, and even water. This represented a considerable challenge, requiring the building of roads (and eventually a railroad) and a network of importers. Because of this, mining towns/cities of the arid Intermountain West often had better connections with the international marketplace than rural Midwestern agrarian communities. Archaeologically, one finds evidence of products from throughout the world: see my book Virginia City: Secrets of a Western Past (2012), which describes over two decades of archaeological investigations of the Virginia City National Historic Landmark District.

To augment what was imported, there was typically a network of ranches, farms, fisheries, etc., that consumed resources for dozens and then hundreds of miles around. This often resulted in the destruction of natural habitats and caused enormous suffering among Native American populations: see Eugene Hattori's excellent essay of Native American adaptation to the Comstock Mining District in my co-edited volume Comstock Women: The Making of a Mining Community (1998).

In the case of Virginia City, there was a large feedlot where cattle were kept (brought in from ranches hundreds of miles around) for regular slaughtering for local markets and restaurants. There was also a well-watered nearby community - American Flat - where farmers raised vegetables for Virginia City. Northern Paiutes at Pyramid Lake operated fisheries that provided additional resources. Many others contributed to this process of gathering and farming for resources for the mining town's markets and restaurants.

While many of the pinyon pine groves were destroyed for firewood in the first two winters (causing further deprivation for Native Americans), those living in the towns quickly developed an appetite for pinyon pine nuts, and the destruction began to decline. With some irony, Native American harvesters often sold the nuts to the city dwellers, because cash became more valuable to them than nuts. Mark Twain - who took his name in Virginia City in 1863 - was known to write friends asking for pinyon pine nuts!

That digression aside, the supply network became expansive, and this approach - written up in mining journals of the day - was imitated internationally. It was an expensive approach (Virginia City's water was piped in over seventeen miles away, for example). The network of roads alone was extensive, and experimentation included using camels to haul supplies (the experiment failed).

One could go on! Feel free to ask questions!

edit: thanks for the precious metals. I'm on my way to become a true Robber Baron of the Gilded Age!

edit #2: It just occurred to me that I have posted chapter 2, dealing with the organization and building of Virginia City - a chapter in my book on the archaeology of the Landmark District; it may be of use to readers.