The valley has a few pronounced relief that is covered with a large clay deposit of up to thick. The lowlands were once part of plain of alluviums of St. Lawrence valley, greater than it is today. In a relatively recent geological time, glaciation changed the relief which subsequently was reduced by sediment deposits dating from the post-glacial of Champlain Sea. The most prominent of the watershed of the river geological formation is also formed by the Monteregian Hills. In addition, nearly half of the banks of the Richelieu River are kept in natural state.