The upper Hyland River area of southeast Yukon is mostly underlain by rocks of the Neoproterozoic-Cambrian Hyland Group. The Yusezyu Formation, which forms the lower part of the Hyland Group, was previously undivided; however, good exposure in the upper Hyland River area facilitates the identification of marker horizons, including marble/limestone layers and thick units of quartz granule-pebble conglomerate. A new 1:50000-scale map of part of the area includes ten stratigraphic subdivisions in rocks previously assigned to the Yusezyu Formation. From northeast to southwest, the structure of the area is characterized by: (1) a southwest-vergent fold and thrust belt; (2) a central region with upright, northwest-trending folds; and (3) a highly deformed region characterized by tight-isoclinal folding, in which folds and stretching lineations are at a high angle to the trend of the orogen. This deformation was accompanied by amphibolite facies, low-pressure metamorphism.
A steeply-dipping fault with long strike-length is coincident with the upper Hyland River valley.