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The trajectory of the map you posted, points toward an area of the country where there are numerous small shallow deposits of gravel. I’ve often wondered how these deposits were formed, when rock to do so is hundreds and hundreds of miles away. I wonder if maybe the impact could have thrown the gravel there from the Great Lakes region? The gravel consists of sedimentary kind of rock with fossilized sea shells and etc., mixed with a little quartz and flint. No limestone or granite, IIRC, to speak of.

Case Closed? Comet Crash Killed Ice Age Beasts "A space rock crashed into Earth about 12,900 years ago, wiping out some of North America's biggest beasts and ushering in a period of extreme cooling, researchers say, based on new evidence supporting this comet-crash scenario. If such an impact took place, it did not leave behind any obvious clues like a crater. But microscopic melted rock formations called spherules and nano-size diamonds in ancient soil layers could be telltale signs of a big collision. The mix of particles could only have formed under extreme temperatures, created by a comet or asteroid impact. Spherules from archaeological sites in the study. The microscopic particles have marred surface patterns from being crystallized in a molten state and then rapidly cooled. Researchers first reported in 2007 that these particles were found at several archaeological sites in layers of sediment 12,900 years old. Now an independent study published in the Sept.17 issue of the Proceedings of the National Academy of Sciences (PNAS) says those findings hold up. A team led by Malcolm LeCompte, of Elizabeth City State University in North Carolina, studied sediment samples from three sites in the Unites States: Blackwater Draw in New Mexico, Topper in South Carolina, and Paw Paw Cove in Maryland. The researchers said they found the same microscopic spherules in some of the same ancient layers as were found in the 2007 study. A comet crash in the ice fields of eastern Canada could explain the region's die-off during the late Pleistocene epoch. While the cause of the catastrophic extinction event has been debated, researchers say it killed off three-fourths of North America's large ice-age animals, such as saber-toothed tigers and woolly mammoths, and the Clovis people, a Stone Age group that had only recently immigrated to the continent. ... "