| Arroyo Las Positas | |
| Name Etymology: | Spanish |
| 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: | Cities |
| Subdivision Name5: | Livermore, Dublin |
| Source1: | confluence |
| Source1 Location: | north of Livermore |
| Source1 Coordinates: | 37.7056°N -121.755°W |
| Source1 Elevation: | 482feet |
| Mouth: | Arroyo Mocho |
| Mouth Location: | north of Dublin |
| Mouth Coordinates: | 37.6947°N -121.8594°W |
| Mouth Elevation: | 348feet |
Arroyo Las Positas is a 7.4adj=midNaNadj=mid[1] westward-flowing watercourse in Alameda County, California, which begins at the confluence of Arroyo Seco and Cayetano Creek north of Livermore, and empties into Arroyo Mocho in Dublin, California.[2]