 The convenient access to transportation provided by the Saginaw River and its numerous tributaries fueled a massive expansion in population and economic activity.As the trees were being cut down in the region, logs were floated down the rivers to sawmills located in Saginaw, destined to be loaded onto ships and later railroad cars.Flint was also a lumber boom town, with the city turning lumber into carriages and wagons, which would later give way to the automobile industry.