A boomtown is a community that undergoes sudden and rapid population and economic growth, or that is started from scratch because of an influx of people. The growth is normally attributed to the nearby discovery of a precious resource such as gold, silver, or oil, although the term can also be applied to communities growing very rapidly for different reasons, such as a proximity to a major metropolitan area, huge construction project, or attractive climate. Early boomtowns, such as Leeds, Liverpool, and Manchester, experienced a dramatic surge in population and economic activity during the Industrial Revolution at the turn of the 19th century. In pre-industrial England these towns had been relative backwaters, compared to the more important market towns of Bristol, Norwich, and York, but they soon became major urban and industrial centres. Although these boomtowns did not directly owe their sudden growth to the discovery of a local natural resource, the factories were set up there to take advantage of the excellent Midlands infrastructure and the availability of large seams of cheap coal for fuel. In the mid-19th century, boomtowns based on natural resources began to proliferate as companies and individuals discovered new mining prospects across the world. The California Gold Rush of the Western United States stimulated numerous boomtowns in that period, as settlements seemed to spring up overnight in the river valleys, mountains, and deserts around what was thought to be valuable gold mining country. In the late 19th and early 20th centuries, boomtowns called mill towns would quickly arise due to sudden expansions in the timber industry; they tended to last the decade or so it took to clearcut nearby forests. Modern-day examples of resource-generated boomtowns include Fort McMurray in Canada, as extraction of nearby oilsands requires a vast number of workers, and Johannesburg in South Africa, based on the gold and diamond trade. The biggest boomtown in the early 21st century is in North Dakota, where oil fields are being exploited.