The Pecos River of southeastern New Mexico and west Texas is among the saltiest rivers in North America with streamflow salinity regularly exceeding 7,000 mg L-1 at the state border and eventually exceeding 12,000 mg L-1 at Girvin, Texas. High salinity of the river has adversely affected stability and biodiversity of the riparian ecosystems as well as the economic uses of this water resource. In addition, a recent study shows that the flow of this river system accounts for nearly one-third of the salts entering the Amistad International Reservoir located at the border to Mexico. These circumstances prompted various attempts to lower salinity, including control of saline water intrusion into the river, and eradication of salt cedars (Tamarix sp). This study was conducted for identifying additional salt sources and river reaches where saline water sources are entering the Pecos River. We first reviewed the historical flow and salinity data of the Pecos River at Malaga and Pierce Canyon (P.C.) Crossing, NM (located near the state border), Girvin and Langtry, TX (the confluence to the Rio Grande). The records show that salinity of the Pecos was around 3,000 mg L-1 at Malaga prior to 1950, and since 1959 averaged 4,100 mg L-1 with greater fluctuation. Salinity at P.C. Crossing during 1938 1940 was 4,800 mg L-1, but increased to 7,100 mg L-1 after 1954 due to the reduced streamflow.