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Spatial and temporal distribution of the radioisotopes concentrations were determined in sediments near the surface and core samples extracted from two reservoirs located in an arid region close to Chihuahua City, Mexico. At San Marcos reservoir one core was studied; while from Luis L. Leon reservoir one core from the entrance and another one close to the wall were investigated. Th-232-series, U-238-series, K-40 and Cs-137 activity concentrations (AC, Bq kg(-1)) were determined by gamma spectrometry with a high purity Ge detector. U-238 and U-234 ACs were obtained by liquid scintillation and.alpha spectrometry with a surface barrier detector. Dating of core sediments was performed applying CRS method to Pb-210 activities. Results were verified by Cs-137 AC. Resulting activity concentrations were compared among corresponding surface and core sediments. High U-238-series AC values were found in sediments from San Marcos reservoir, because this site is located close to the Victorino uranium deposit. Low AC values found in Luis L Leon reservoir suggest that the uranium present in the source of the Sacramento Chuviscar Rivers is not transported up to the Conchos River. Activity ratios (AR) U-234/U-238 and U-238/Ra-226 in sediments have values between 0.9-1.2, showing a behavior close to radioactive equilibrium in the entire basin. U-234/U-238 and U-238/Ra-226 ARs are witnesses of the different geological origin of sediments from San Marcos and Luis L. Leon reservoirs.