and a fairly thin lower level consisting of stacked imbricate, southwest-facing, sigmoidal thrust fault slices, bounded below by the Lewis thrust, and above by a separate bedding-parallel thrust called the Tombstone thrust. These culminations progressively stack up and accommodate significant lateral crustal shortening associated with the compression along the Lewis thrust fault. Another extremely similar section of this duplexing is seen at another outcrop in the Waterton Lakes area in Southwest Alberta. In addition to duplexes seen in windows, the Lewis thrust also shows isolated remnants of the eastern edge of the upper plate( klippes) located at Chief Mountain in Montana and Crowsnest Mountain in Alberta. Erosion over time has shaped the mountains into their characteristic shape, where they tower over the associated prairies. Geochronology The fault motion of the Lewis thrust is dated based on the oldest age for motion being defined by the youngest sediments on the footwall, which are said to be about 65 million years old. Fission track analysis of Uranium-bearing minerals such as Zircons and Apatite which involves dating the radioactive uranium found in sediments along the Lewis thrust using isotopic ratios of Uranium provides constraints of the late pre-deformational paleogeothermal gradient and thickness of the Lewis sheet. This data, after being calibrated into geologic ages, led to the conclusion that maximum burial and heating in the Lewis thrust occurred during the Campanian over a time interval of less than 15 million years prior to the start of movement of the thrust sheet. The Apatite fission track data showed abrupt change in paleotemperatures from high to low temperatures and associated changes in uranium concentrations as burial and heating came to a halt and movement and exhumation began, which showed that displacement of Mesoproterozoic strata of the Belt–Purcell Supergroup along the Lewis thrust fault was in motion by approximately 75 Ma. This is supported by locations further south along the thrust fault in Montana where faults on the leading edge cut through a 76 Ma volcanic marker proving that the onset of fault movement must be younger than 76 Ma. The Youngest movement along the fault or in other words, the end of movement for thrust movement is based on the stratigraphic and structural characteristics of early Eocene deposits and is limited by the age of normal faults that cut the thrust and the associated sediments found within these normal faults. Additionally, The cooling of the