She first thought it was a piece of glass and did not realize what she had found until the rock was identified by park staff.
The park allows the public to search and keep diamonds found on the grounds. More than 33,100 diamonds have been found since it became a state park in 1972.
The woman named the diamond Lichtenfels, which means “a rock between two lights,” in honor of her hometown in Germany, KHBS reported.
The woman was standing between her grandchildren when she made the find.