4 USGS Streamgages
Santa Ana River flows and levels
Santa Ana River is gauged at 4 USGS streamgages in California, each tracked by Rivermatics. The mainstem runs about 101 miles (163 km) from headwaters to outlet. It drains roughly 2,373 square miles at its outlet. The gauged reach falls about 1,505 feet, from 1,956 feet down to 452. Rivermatics issues a daily machine-learned 14-day flow outlook at 3 of them.
Gauges on this river, upstream to downstream
Ordered by drainage area, which is how far down the river each gauge sits. April and July figures are long-term median daily flows for that month from the USGS record — historical normals, not a forecast and not today's reading.
| Gauge | State | Drainage sq mi | Elevation ft | April p50 cfs | July p50 cfs | Forecast |
|---|---|---|---|---|---|---|
| Santa Ana River near Mentone (River Only), CA | CA | 210 | 1,956 | 29.1 | 0.2 | 14-day |
| Santa Ana River near Mentone, CA | CA | 210 | 1,950 | 19.3 | 1.9 | 14-day |
| Santa Ana River below Prado Dam, CA | CA | 2,258 | 452 | 190.4 | 93 | 14-day |
| Santa Ana River near Mentone Cn + Cn, CA | CA | — | — | 70.8 | 46.1 | — |
Typical flow by month at Santa Ana River near Mentone Cn + Cn, CA
The furthest-downstream gauge on this river, so the fullest flow it carries here. Long-term daily discharge percentiles from the USGS record (up to 114 years of data), averaged within each month. These describe the historical normal range — they are not a forecast and not today's reading.
| Month | Low p10 | Typical p50 | High p90 | Range |
|---|---|---|---|---|
| January | 19.8 | 36.7 | 115.8 | |
| February | 21.4 | 48.7 | 204.5 | |
| March | 26.8 | 58 | 273.6 | |
| April | 29.7 | 70.8 | 286.3 | |
| May | 24.4 | 56.1 | 236.8 | |
| June | 16.7 | 47 | 163.4 | |
| July | 12.4 | 46.1 | 119.6 | |
| August | 12.9 | 44.2 | 95.1 | |
| September | 13.2 | 41.5 | 86.9 | |
| October | 15.3 | 38 | 79.8 | |
| November | 17.3 | 32.8 | 69.3 | |
| December | 18.6 | 33.2 | 76.5 |
All values in cubic feet per second (cfs).
Common questions
- When does the Santa Ana River run highest?
- April, on the long-term record at Santa Ana River near Mentone Cn + Cn, CA — the furthest-downstream gauge Rivermatics tracks on this river. Median daily flow there is about 70.8 cfs that month, against 32.8 cfs in November, the lowest. Upstream gauges peak on their own schedule; the table on this page gives April and July for each.
- How many gauges are on the Santa Ana River?
- Rivermatics tracks 4 USGS streamgages on the Santa Ana River, across California. Each has its own page with the site's full flow record and monthly normals. The river may carry other gauges that publish neither daily values nor discharge statistics; those are not tracked here.
- Is there a flow forecast for the Santa Ana River?
- Yes, at 3 of the 4 gauges. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on each basin's observed flows, weather and snowpack, and issues a daily outlook reaching 14 days ahead: a median estimate inside a confidence band, not a single number to bet on. Every forecast is scored against days the model never trained on, and that track record is published on each gauge's live screen.
- Can I use Santa Ana River data for flood or safety decisions?
- No. Rivermatics provides estimates, not guarantees, and the readings and forecasts here may be delayed, inaccurate, or wrong. Do not use them for navigation or for any safety, rescue, or emergency decision. Check the National Weather Service and USGS directly, and use your own judgment.