The 6 December 2025 moment magnitude (Mw) 7.0 earthquake in southwestern Yukon was the largest onshore earthquake in Canada in over 75 years. Although it caused no casualties or damage to the built environment, the event provides important insight into the active tectonics of southwestern Yukon and neighbouring Alaska. We developed a new earthquake catalog using machine learning detection and phase picking algorithms, identifying over 8,500 events associated with the aftershock sequence following the main event. We applied double-difference relocation to refine aftershock locations and illuminate the detailed rupture geometry. Moment tensors were calculated for all events M≥5.0, while probabilistic focal mechanisms were determined for earthquakes between M3.0 and M5.0, providing comprehensive constraints on fault kinematics and the local stress field. The relocated seismicity and event mechanisms indicate that rupture may have involved activation of multiple faults. We infer that the earthquake ruptured the southernmost section of the hypothesized Totschunda–Fairweather Connector fault. Slip initiated as strike-slip motion, propagated northwestward, and activated a conjugate reverse fault toward the northwestern portion of the rupture zone. We examine the Coulomb stress transfer and evaluate changes in loading on nearby and adjacent fault segments. Together, these observations improve our understanding of this major Yukon fault system, as well as earthquake hazard in a remote but actively deforming plate-boundary region.