I’m not able to ID based on the photos but if found in Webster, SD then it is Pleistocene glacial till.
https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=SDQlts;0
I would also advise people collecting in this area to be aware of where exactly they are collecting because Webster is very near the Lake Traverse Reservation and collecting there is limited to Native Americans and those individuals who have received permission from the tribe and/or the Native American landowner.