| Arroyo Seco | |
| Pushpin Map: | USA California |
| Pushpin Map Caption: | Location of the mouth in California |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | California |
| Subdivision Type3: | Region |
| Subdivision Name3: | Alameda County |
| Subdivision Type5: | City |
| Subdivision Name5: | Livermore |
| Source1: | spring |
| Source1 Location: | 8-1NaN-1 southeast of Livermore |
| Source1 Coordinates: | 37.6658°N -121.6142°W |
| Source1 Elevation: | 1990feet |
| Mouth: | Arroyo Las Positas |
| Mouth Location: | north of Livermore |
| Mouth Coordinates: | 37.7056°N -121.7564°W |
| Mouth Elevation: | 482feet |
Arroyo Seco is an 11.7adj=midNaNadj=mid[1] watercourse in Alameda County, California, that traverses through the city of Livermore, emptying into Arroyo Las Positas. Arroyo Seco means "dry stream" in Spanish. Arroyo Seco lies above the Arroyo Seco watershed, which includes the eastern part of the city of Livermore and also the Sandia National Laboratory. The Mocho Subbasin is the largest of the subbasins in the Livermore Valley watershed. This subbasin is bounded to the west by the Livermore Fault Zone and to the east by the Tesla Fault. Some groundwater flow occurs across these fault boundaries, but flows are discontinuous below a depth of across the Tesla Fault and south of the Arroyo Mocho channel across the Livermore Fault.[2] A number of threatened and endangered species reside in this watershed.[3]