The study area is comprised of three primary rock units including the Valley Spring Gneiss, the Lost Creek Gneiss and the Packsaddle Schist (Fig. 2). The Valley Spring Gneiss consists of quartzofeldspathic gneisses and some pelitic sillimanite-rich schists with supracrustal and plutonic rock protoliths. These units are interpreted to represent a continental margin arc, as well as some terrigenous clastics and basement rocks (Mosher, 1998; Reese et al., 2000). The Lost Creek Gneiss is a medium-coarse grained augen gneiss, interpreted to be a deformed granitic pluton, which intruded between the Valley Spring Gneiss and the Packsaddle Schist before Grenville-age orogenesis began. The Packsaddle Schist is a very heterogenous assemblage of rock types, including quartzofeldspathic gneisses, amphibolites and minor marbles and calc-silicates, with both supracrustal and intrusive rock protoliths. The Valley Spring Gneiss is at the highest structural level and the Packsaddle Schist is deepest in the orogenic pile in the western Uplift (Fig. 2).

Six phases of deformation (D₁-D₆) produced local- to regional-scale folding (F₁-F₅) and fabrics (S₁-S₅) under uppermost amphibolite facies conditions, as evidenced by the presence of sillimanite and potassium feldspar in equilibrium. _D1-D3 are constrained between 1254 +6/-4 Ma and 1126 +5/-4 Ma; D₄ and D₅ between 1126 +5/-4 Ma and 1076 ± 5 Ma (Roback et al., 1999; Hunt, 2000).

D₁ and D₂ produced isoclinal folds with well-developed axial planar foliations parallel to compositional layering (S₀). F₁ folds are rarely observed in the field but have been identified within the hinges of F₂ folds in thin section. F₂ folds fold a pronounced metamorphic foliation (S₁) and plunge easterly; _S1/S2 composite fabrics dip north to southeast. This variation in orientation is due to later refolding of the composite _S1/S2 foliation. F₃ folds are upright to inclined, tight folds with southeast plunging fold axes and an S₃ foliation oriented oblique to _S1/S2 fabrics. The S₃ foliation is less well developed than the dominant _S1/S2 fabric, and is commonly defined by aligned biotite, sillimanite or leucosomes. F₄ and F₅ folds are open folds that refold all previous folds on an outcrop- to regional-scale and contain axial planar fabrics. F₄ folds have northeast to east striking axial planes, whereas F₅ folds have northwest striking axial planes with southeast plunging fold axes. In some areas it is possible to find a poorly developed axial planar foliation associated with these late open folds. Local late extension and shear zones (D₆) occurred, partly, synchronous with granite dikes dated by U-Pb geochronology at ca. 1076 Ma (Roback et al., 1999). Granitic and pegmatitic intrusions increase from west to east and are syn- to post- deformational.

The eastern and western portions of the uplift have opposite senses of structural stacking and differing kinematics in all but the D₅ structures. The eastern uplift has a northeast-directed tectonic transport and the lithotectonic domain boundaries are defined by large-scale shear and an increased intensity of deformation. In contrast, the western uplift has a southwesterly direction of tectonic transport and the domain boundaries are not characterized by any large-scale shear zones or increased intensity of deformation. We interpret this disparity to be the result of differences in structural depth within the orogen and to the presence of an exotic island arc in the eastern uplift (Roback, 1996). In the eastern uplift, the structures are locally dominated by collision of the exotic arc and Laurentia, whereas the western uplift is deeper in the orogenic pile and records continent-continent collision without an intervening arc (Fig. 3).