By combining terrace riser offsets with terrace ages dated by 14C, optically stimulated luminescence (OSL), and 10Be techniques, we determine average slip rates of 1.1 ± 0.3 mm/yr and 1.2 ± 0.4 mm/yr for the Elashan and Riyueshan faults, two north-northwest–trending, right-lateral, strike-slip faults west and east of the lake Qinghai in the northeastern margin of the Tibetan Plateau. These faults are conjugate to the major easterly trending, left-lateral Altyn Tagh, Haiyuan-Qilianshan, and Kunlun faults, and they contribute to the subdivision of the region between the Haiyuan-Qilianshan and Kunlun faults into small blocks tens to ∼100 km in dimension. The relatively low slip rates in this region reflect distributed deformation. The total right-lateral offsets of geological contacts are ∼9–12 km along the Elashan fault and ∼11–12 km for the northern segment of the Riyueshan fault. If long-term slip rates were constant during late Cenozoic time, dates of initiation of dextral movement would be 9 or 10 ± 3 Ma for the two strike-slip faults, concurrent with onsets or acceleration of tectonic deformation in Cenozoic basins nearby. Our study highlights a stage of tectonic deformation in the northeastern margin of the Tibetan Plateau beginning since ca. 8–12 Ma, tens of millions of years after the collision between India and Eurasia began.