Abstract: This study aims to reveal the source of salts in the soda saline-alkali land in the western Songnen Plain. Focusing on Taonan City under the administration of Baicheng City in Jilin Province, this study systematically investigated the weathering and saline-alkali ion release characteristics of pyroclastic rocks, granites, and sandstones along the eastern margin of the Great Xing'an Range. The results indicate that rocks in the study area remain in the early-to-middle stage of chemical weathering, predominantly releasing Ca, K, Na, and Si. The loss of saline-alkali ions per unit mass of the rocks decreases in the order of pyroclastic rocks, sandstones, and granites. When migrating from high-elevation hills to low-lying plains, groundwater is enriched in substantial Na⁺ and HCO₃⁻, accompanied by a slight increase in the K⁺ content and loss of Ca²⁺, SO₄²⁻, Cl⁻, and Mg²⁺ ions, with the pH value elevated. The results demonstrate that the weathering of plagioclases in pyroclastic rocks contributes largely to salinization and alkalization. Furthermore, the early-to-middle chemical weathering represents the key process of the release of saline-alkali ions, while topography-driven water and salt migration emerges as the dominant path of ion enrichment. The results of this study provide a scientific basis for the precise prevention and control of regional saline-alkali land and ecological restoration.