I am pretty sure that since the begining of time, people were burying their valuables...Not trying to be a smart a** or anything...hahah
You are in Michigan, correct? During the Depression everyone buried their money or hid it as they didnt trust banks . So look at the 1930's time line.
The Michigan electorate organized a government without U.S. sanction and in 1836 operated as a state, although outside the Union
The Ojibwa, the Ottawa, the Potawatomi, Native American groups were living in Michigan when the French explorer ?tienne Brul? landed at the narrows of Sault Ste. Marie in 1618. Later French explorers, traders, and missionaries came, including Jean Nicolet, who was searching for the Northwest Passage; Jacques Marquette, who founded a mission in the Mackinac region; and the empire builder, Robert Cavelier, sieur de La Salle, who came on the Griffon, the first ship to sail the Great Lakes. French posts were scattered along the lakes and the rivers, and Mackinac Island (in the Straits of Mackinac) became a center of the fur trade. Fort Pontchartrain, later Detroit, was founded in 1701 by Antoine de la Mothe Cadillac. The vast region was weakly held by France until lost to Great Britain in the last conflict (1754?63) of the French and Indian Wars.
So you would probally do well to search old fort sites and areas as well.
There are so many older cities scattered through out Michigan, that any of the renovation areas are worth digging at.
Rumor has it that The underground railroad ran flat smack through some of the river towns,....Niles ,Bertrand,ST Joseph, New Buffalo, Benton Harbor .
Allegan has many older ,forgotton sites as well.
try around the old train depots and the harbors . The ferry harbor is a great place to dig as well as near Mackinaw bridge .
I Know that the KKK had a large contingencty near Galean ...artifacts ?
Good Luck !!! :P