Bedrock of the upper Esopus is generally sedimentary rock of the middle to late Devonian period, deposited when today's Catskills were a river delta and alluvial plain 360-390 million years ago.
The stream's uppermost headwaters are underlain by bedrock of the Slide Mountain Formation, a Frasnian cross-bedded yellowish-gray conglomerate layer with quartz pebbles found at the uppermost 2,000 feet (610 m) in the Catskills.
It is the youngest of the sediment layers in the mountains, deposited shortly before the entire region uplifted to form the dissected plateau it is today.

Not far below Winnisook Lake, the Slide Mountain formation gradually gives way to the Upper Walton Formation, characterized by gray and greenish-gray fine-grained sandstone with some pebbles like those seen in the stratum above.
The Upper Walton soon gives way, by the point the creek receives Giant Ledge Stream, to the Lower Walton, with fine-grained sandstone and some gray shale.
This layer remains the Esopus's bedrock all the way to the Bushnellsville Creek confluence.

At that point the Oneonta Formation takes over for the rest of the upper Esopus.
The Oneonta's bedrock is more coarse-grained cross-bedded lighter gray sandstone with some red shale beds.
Siltstones and claystones are also present.

Below the Ashokan Reservoir, the Catskill sediments continue to underlie the lower Esopus, this time in the form of the region's lowest and oldest layer, the Givetian Plattekill Formation.
It is characterized by grayish-red claystone and shale interbedded with medium dark gray shale and cross-bedded sandstone.

Just above its bend to the northeast at Marbletown, the Catskill sediments end, giving way to the limestone underneath the broad flood plains to Kingston.
This reach continues north of the city, with oxbow lakes and meander scroll indicating the occurrence of many active floods in the recent past.
North of Leggs Mill Road the bedrock changes again to tightly folded shale as the Esopus drops through a fault at Glenerie Falls and into the narrow valley, itself a fault between shale and the limestone layers on the adjoining ridges, that takes it to its mouth at Saugerties.

The Esopus's surficial geology reflects the effect of past glaciations on the Catskills.
It begins with glacial till covering the bedrock at the stream's steep uppermost reaches, giving way to kame deposits on the north bank for another short stretch and then till again.
At Allaben outwash sand and gravel takes over.
The streambed rocks are generally imbricated, keeping them stable except in heavy floods.

Below the reservoir, the outwash gives way in some areas to sand barrens.
The fertile soils of the many farms alongside the creek characterize the surface of the floodplain reach.
The lower reach, once part of the glacial Lake Albany, still has the clays and silt from its days as a lake bottom.
Bedrock of the upper Esopus is generally sedimentary rock of the middle to late Devonian period, deposited when today's Catskills were a river delta and alluvial plain 360-390 million years ago. The stream's uppermost headwaters are underlain by bedrock of the Slide Mountain Formation, a Frasnian cross-bedded yellowish-gray conglomerate layer with quartz pebbles found at the uppermost 2,000 feet (610 m) in the Catskills. It is the youngest of the sediment layers in the mountains, deposited shortly before the entire region uplifted to form the dissected plateau it is today.
Not far below Winnisook Lake, the Slide Mountain formation gradually gives way to the Upper Walton Formation, characterized by gray and greenish-gray fine-grained sandstone with some pebbles like those seen in the stratum above. The Upper Walton soon gives way, by the point the creek receives Giant Ledge Stream, to the Lower Walton, with fine-grained sandstone and some gray shale. This layer remains the Esopus's bedrock all the way to the Bushnellsville Creek confluence.
At that point the Oneonta Formation takes over for the rest of the upper Esopus. The Oneonta's bedrock is more coarse-grained cross-bedded lighter gray sandstone with some red shale beds. Siltstones and claystones are also present.
Below the Ashokan Reservoir, the Catskill sediments continue to underlie the lower Esopus, this time in the form of the region's lowest and oldest layer, the Givetian Plattekill Formation. It is characterized by grayish-red claystone and shale interbedded with medium dark gray shale and cross-bedded sandstone.
Just above its bend to the northeast at Marbletown, the Catskill sediments end, giving way to the limestone underneath the broad flood plains to Kingston. This reach continues north of the city, with oxbow lakes and meander scroll indicating the occurrence of many active floods in the recent past. North of Leggs Mill Road the bedrock changes again to tightly folded shale as the Esopus drops through a fault at Glenerie Falls and into the narrow valley, itself a fault between shale and the limestone layers on the adjoining ridges, that takes it to its mouth at Saugerties.
The Esopus's surficial geology reflects the effect of past glaciations on the Catskills. It begins with glacial till covering the bedrock at the stream's steep uppermost reaches, giving way to kame deposits on the north bank for another short stretch and then till again. At Allaben outwash sand and gravel takes over. The streambed rocks are generally imbricated, keeping them stable except in heavy floods.
Below the reservoir, the outwash gives way in some areas to sand barrens. The fertile soils of the many farms alongside the creek characterize the surface of the floodplain reach. The lower reach, once part of the glacial Lake Albany, still has the clays and silt from its days as a lake bottom.
Esopus Creek