Geology thumb|left|The geology of Yorkshire including the River Derwent catchment area At its source on the North York Moors the River Derwent and its tributaries run over Corallian Limestone from the Jurassic period. Downstream of Stamford Bridge the catchment area is mainly of Sherwood Sandstone from the Triassic period. To the east this sandstone dips under Mercia Mudstone, also of the Triassic period. Some of the underlying rocks are major aquifers and provide a valuable source for water supply in the area. The major aquifers are the Corallian limestone, chalk and Sherwood sandstone. The Corallian Limestone outcrops on the hills surrounding the Vale of Pickering and is made up of a series of limestones and sandstones. This aquifer is unconfined in parts and gets water from the River Rye and River Derwent through swallow holes.
Geology thumb|left|The geology of Yorkshire including the River Derwent catchment area At its source on the North York Moors the River Derwent and its tributaries run over Corallian Limestone from the Jurassic period. Downstream of Stamford Bridge the catchment area is mainly of Sherwood Sandstone from the Triassic period. To the east this sandstone dips under Mercia Mudstone also of the Triassic period. Some of the underlying rocks are major aquifers and provide a valuable source for water supply in the area. The major aquifers are the Corallian limestone, chalk and Sherwood sandstone The Corallian Limestone outcrops on the hills surrounding the Vale of Pickering and is made up of a series of limestones and sandstones. This aquifer is unconfined in parts and gets water from the River Rye and River Derwent through swallow holes.