Sediment traps were deployed in thirty-three ephemeral and perennial tributaries to the San Juan River during 2021 and 2022. This dataset includes the chemical concentrations of the sediment samples collected in sediment traps during storm events. These traps collected sediment during storm events that typically occur as monsoonal convective storms from June to September. Because of the rural nature of the watershed, sediment traps were collected every 3 weeks so the sediment collected is a composite of that time period. The date listed is the date the trap was collected. Major ions are reported in weight percentage, while all other elements are reported in parts per million. Each sample was split and analyzed following two different methods of sample preparation. In one method, the sample is decomposed using a mixture of hydrochloric, nitric, perchloric, and hydrofluoric acids at low temperature. In the second method, samples are fused at 750°C with sodium peroxide and the fusion cake dissolved in a dilute nitric acid. The resulting solution for both methods is analyzed by ICP-OES and ICP-MS.