Suffield Memorandum 49/67 records the 11 August 1967 onsite inspection, measurements, grass condition, radiation checks and possible mechanical or human explanations for four rings near Duhamel.
This is the principal source because it distinguishes measured ground marks from later claims that a craft was directly observed landing.
No craft was witnessed, radiation was normal and the report did not reach a conclusive cause. The rings are documented traces, not verified UFO landing evidence. Original source: https://www.bac-lac.gc.ca/eng/discover/unusual/ufo/Documents/Duhamel-inspection-report.pdf