North Dakota has added about 100,000 workers since 2009, leading the nation in population growth. Moreover, many of those new residents are male: "From 2009 to 2013, the number of men in North Dakota increased by 14% (46,000), compared with a 9% increase among women (30,000)." Hence the term, "man rush."
Given the current energy and population boom in North Dakota, the Pew Research Center, "thought back to the late 1800s with the silver rush in Colorado and Alaska’s oil boom in the 1970s, and then examined census data from those periods. It turns out that North Dakota’s population boom is not nearly as large as these two other moments in history."