Given the following context:  Ricketts Glen State Park is in five townships in three counties. After the 1768 purchase, the land became part of Northumberland County, but was soon divided among other counties. Most of the park is in Luzerne County, which was formed in 1786 from part of Northumberland County. Within Luzerne County, the majority of the park, including all of the waterfalls and most of Lake Jean, is in Fairmount Township, which was settled in 1792 and incorporated in 1834; the easternmost part of the park is in Ross Township, which was settled in 1795 and incorporated in 1842. The northwest part of the park is in Sullivan County, which was formed in 1847 from Lycoming County; Davidson Township was settled by 1808 and incorporated in 1833, while Colley Township, which has the park office and part of Lake Jean, was settled in the early 19th century and incorporated in 1849. A small part of the southwest part of the park is in Sugarloaf Township in Columbia County; the township was settled in 1792 and incorporated in 1812, the next year Columbia County was formed from Northumberland County.A hunter named Robinson was the first inhabitant in the area whose name is known; around 1800 he had a cabin on the shores of Long Pond (now called Lake Ganoga), which is less than 0.4 miles (0.6 km) northwest of the park. The first development within the park was the construction of the Susquehanna and Tioga Turnpike, which was built from 1822 to 1827 between the Pennsylvania communities of Berwick in the south and Towanda in the north. The turnpike, which Pennsylvania Route 487 mostly follows through the park, had daily stagecoach service from 1827 to 1851; the northbound stagecoach left Berwick in the morning and stopped for lunch at the Long Pond Tavern on the lake about noon.The earliest settlers in what became the park were two squatters who built sawmills to make bed frames from cherry trees they cut for lumber. One squatter, Jesse Dodson, cut trees from around 1830 to 1860 and built a mill and the dam for what became Lake Rose in...  answer the following question:  What were the two structures built by Dodson?
A:
a dam