Two men in row boat, a tug boat (the Marion), and a barge heaped with clams on the shore of the St. Croix River at Afton, Minnesota. In the drought year of 1911, the river channel was often, in places, no more than twenty feet wide. That was the year towns people reaped a harvest of clams. They did not eat the clams; they searched them for pearls. A gem quality pearl, pink, white, blue, or purple, the size of a pea, brought $100 or more. The imperfect pearls were called slugs.