Abstract: The modal analysis of the sandstone framework minerals in the Upper Ganchaigou and Lower Ganchaigou formations at Height 3 of the Hongsanhan No. 1 area, western Qaidam basin, suggests that the provenance of Eocene-Oligocene sandstones is mainly a recyclic orogenic zone. According to the paleocurrents, it is inferred that the provenance is mainly the Altyn Tagh Mountains. Based on the triangular discrimination diagrams of sandstones showing the standard deviation polygons for the Upper Ganchaigou and Lower Ganchaigou formations in the Hongsanhan area and variations of the average framework mineral compositions of sandstones, differences between the Upper Ganchaigou and Lower Ganchaigou formations may be observed, which shows that the Altyn Tagh Mountains began to be uplifted in the Oligocene (Upper Ganchaigou Formation).