Electroforming and resistive switching in SiO₂ materials are investigated by controlling the annealing temperature, etching time and operating ambient. Thermal anneal in reducing ambient lowers electroforming voltage to <10 V, providing insight into possible electroformation precursors. Conductive filaments form within ∼4 nm of sidewall surfaces in devices with an etched SiO₂ layer, whereas most filaments are >10 nm from the electrode edge in devices with continuous SiO₂ layers. Switching unpassivated devices fails in 1 atm air and pure O₂/N₂, with the recovery of vacuum switching at ∼4.6 V after switching attempts in O₂/N₂ and at ∼9.5 V after switching attempts in air. Incorporating a hermetic passivation layer enables switching in 1 atm air. Discussions of defect energetics and electrochemical reactions lead to a localized switching model describing device switching dynamics. Low-frequency noise data are consistent with charge transport through electron-trapping defects. Low-resistance-state current for <1.5 V bias is modeled by hopping conduction. A current “overshoot” phenomenon with threshold near 1.6 V is modeled as electron tunneling. Results demonstrate that SiO₂-based resistive memory devices provide a good experimental platform to study SiO₂ defects. The described electroforming methods and operating models may aid development of future SiO₂-based resistive memory products.