 After initial glacial retreat at around 13,000 years ago a saltwater fjord occupied this basin when relative sea levels were still ca 120 to 140m above current levels in the region.Unlike neighbouring Indian Arm and Howe Sound farther west, this fjord basin became partly cut off from tidal waters by sedimentation of the lower Fraser River ca 10,500 years ago, and Pitt Lake is now considered a tidal fjord lake.The mountain range on its east flank comprises Golden Ears Provincial Park, its basin to the north is in southern Garibaldi Provincial Park, while the mountain range on its west, northeast of Vancouver's Coquitlam Lake watershed reservoir, is Pinecone Burke Provincial Park.