Beneath Point Roberts, the bedrock of the Chuckanut Formation was deposited as an alluvial plain containing layers of sediments consisting of silt, sand, sand and gravel, and peat.
During the last 60 million years the sediments were compacted and folded by mountain building forces from continental drift to form strata of siltstone, sandstone, conglomerate and coal.
During recent geologic history, the Chuckanut formation was overridden by four or more glaciations.

Point Roberts consists of a series of the resulting glacial sediments resting upon the Chuckanut Formation.
The lowest glacial sediments (now near sea level) are from Salmon Springs or older glaciations.
At the peak of the most recent glaciation, the main ice sheet was in excess of 7,000 feet thick as it moved southward between Vancouver Island and the Canadian Coast Range and down the Strait of Georgia.
 A smaller lobe of the continental glacier in excess of 5,000 feet traveled down the Fraser River flood plains merging with the main ice sheet over the greater Vancouver area and Whatcom and Skagit Counties.
The coalesced continental ice sheet traveled south terminating in the vicinity of Chehalis, Washington.
 Relatively impermeable Vashon glacial lodgment till (estimated to be as much as 40 feet thick at the uppermost layer) was plastered over the advance outwash as the weight of the 7,000 foot thick plus Strait of Georgia ice lobe moved southward over approximately 10,000 years. (
Armstrong, et al.,
1965)  Point Roberts, Tsawwassen, and part of British Columbia extending past English Bluff comprised an island at the close of the Vashon Glaciation, approximately 11,000 years ago.

As the ice sheets melted, the thinner Fraser Lobe began to float while the Strait of Georgia lobe acted as a dam forming a lake under the Fraser Lobe.
Sediments settling from the melting, floating ice resulted in the accumulation of 300 feet or more of Glacial Marine Drift over much of western Whatcom County. (
Easterbrook, 1976; Geologic Map of Western Whatcom County, Washington, USGS, Map I-854-B)  This Glacial Marine Drift is generally soft and was not consolidated by the weight of the glacier.
 A discontinuous, thin mantle of this Glacial Marine Drift above the Glacial Lodgment Till has been identified sporadically across Point Roberts.
 The uppermost layer of glacial sediments consists of recessional sand, silt, and gravel deposited as the Strait of Georgia ice lobe receded.
 Since the recession of the glaciers, the Fraser River has deposited deltaic sediments on the north and easterly side of the Point Roberts-Tsawwassen Island connecting it to the Greater Vancouver mainland (approximately 2,500 years ago, Murray 2008).
 At some locations, these sediments have been eroded or removed exposing the lodgment till.
Beneath Point Roberts, the bedrock of the Chuckanut Formation was deposited as an alluvial plain containing layers of sediments consisting of silt, sand, sand and gravel, and peat. During the last 60 million years the sediments were compacted and folded by mountain building forces from continental drift to form strata of siltstone, sandstone, conglomerate and coal. During recent geologic history, the Chuckanut formation was overridden by four or more glaciations.
Point Roberts consists of a series of the resulting glacial sediments resting upon the Chuckanut Formation. The lowest glacial sediments (now near sea level) are from Salmon Springs or older glaciations. At the peak of the most recent glaciation, the main ice sheet was in excess of 7,000 feet thick as it moved southward between Vancouver Island and the Canadian Coast Range and down the Strait of Georgia.  A smaller lobe of the continental glacier in excess of 5,000 feet traveled down the Fraser River flood plains merging with the main ice sheet over the greater Vancouver area and Whatcom and Skagit Counties. The coalesced continental ice sheet traveled south terminating in the vicinity of Chehalis, Washington.  Relatively impermeable Vashon glacial lodgment till (estimated to be as much as 40 feet thick at the uppermost layer) was plastered over the advance outwash as the weight of the 7,000 foot thick plus Strait of Georgia ice lobe moved southward over approximately 10,000 years. (Armstrong, et al., 1965)  Point Roberts, Tsawwassen, and part of British Columbia extending past English Bluff comprised an island at the close of the Vashon Glaciation, approximately 11,000 years ago.
As the ice sheets melted, the thinner Fraser Lobe began to float while the Strait of Georgia lobe acted as a dam forming a lake under the Fraser Lobe. Sediments settling from the melting, floating ice resulted in the accumulation of 300 feet or more of Glacial Marine Drift over much of western Whatcom County. (Easterbrook, 1976; Geologic Map of Western Whatcom County, Washington, USGS, Map I-854-B)  This Glacial Marine Drift is generally soft and was not consolidated by the weight of the glacier.  A discontinuous, thin mantle of this Glacial Marine Drift above the Glacial Lodgment Till has been identified sporadically across Point Roberts.  The uppermost layer of glacial sediments consists of recessional sand, silt, and gravel deposited as the Strait of Georgia ice lobe receded.  Since the recession of the glaciers, the Fraser River has deposited deltaic sediments on the north and easterly side of the Point Roberts-Tsawwassen Island connecting it to the Greater Vancouver mainland (approximately 2,500 years ago, Murray 2008).  At some locations, these sediments have been eroded or removed exposing the lodgment till.
Point Roberts, Washington