Abstract This trip focuses on the kinematics, timing, and tectonic significance of a system of Proterozoic ductile shear zones that localized Paleozoic to Tertiary faults, plutons, and ore deposits within the Colorado mineral belt. The nearly two billion year history of tectonism, magmatism, and mineralization in the Colorado mineral belt suggests that this zone has acted as a persistent weakness in the lithosphere that has been reactivated repeatedly. Field, petrologic, and geochronologic evidence indicates that this lithospheric weakness originated as a high strain zone during Early Proterozoic assembly of the continent and evolved into an intracontinental shear zone system during the Middle Proterozoic. The trip consists of three short hikes and, time permitting, several shorter roadside stops in the central Front Range and northern Sawatch Range. We will visit the Idaho Springs–Ralston and Homestake shear zones and compare and contrast these two shear zones and their tectonic histories. Field observations illustrate how the shear zones developed as broad high-T ductile shear zones during the assembly of the continent (1.8–1.6 Ga), how they were reactivated as mylonite zones during ca. 1.4 Ga intracontinental tectonism, and how they have continued to evolve as brittle faults and conduits for magmatic and hydrothermal fluids during the Phanerozoic. The stops were chosen to stimulate discussions about the mechanisms of shear zone localization and reactivation and how such processes fit into models for continental lithospheric evolution. In particular, we will examine how high-strain zones that are originally formed during continental assembly can persist as weaknesses in the continental lithosphere for billions of years and influence the tectonic evolution of continental interiors.