Analyze the brief flowering & decline of the cattle & mining frontiers.
The cattle and mining frontiers "flowered" briefly and then ended as "civilization" spread out further into the West.
These frontiers were made possible by the extension of railroads after the Civil War. the railroads, for example, allowed the cattle to be driven from the frontiers to towns on railheads where they could be shipped east.
These frontiers ended, though, as settlers filled the West. This was especially true of the cattle frontier. It died off as settlers came, fencing the ranges to protect their farms and bringing an end to the era of cattle drives and cowboys.