After the railroad came to the county, the population began to expand more rapidly and non-Mormons began to settle in Salt Lake City. During the early 20th century, heavy industry came to the valley as well, diversifying its economy. Local and interurban trolley systems were built covering the more urban northeastern quarter of the valley. The city dismantled the trolley system by 1945, favoring the use of individual cars. Throughout the late 19th and early 20th centuries, the east side of the valley began to be more densely settled.