USGS Streamgage 11046000
Santa Margarita River A Ysidora, CA
Santa Margarita River A Ysidora, CA is USGS streamgage 11046000 in California, monitoring river discharge in hydrologic subbasin 18070302. It drains a watershed of about 723 square miles. Discharge records at this site go back to 1923. Typical flow runs near 0.8 cfs in July and 16.7 cfs in April, with the higher of the two arriving in April. Rivermatics issues a daily machine-learned flow outlook for this gauge, reaching 14 days ahead.
View live conditions & forecast →
Gauge details
- State
- California
- Drainage area
- 723 sq mi
- Gauge elevation
- 70 ft
- Subbasin (HUC-8)
- 18070302
- Coordinates
- 33.31114, -117.34726
- USGS site number
- 11046000
- Records begin
- 1923-03-01 (103 years)
- Rivermatics forecast
- 14-day flow outlook
14-day flow forecast
Based on observations through for Santa Margarita River A Ysidora, CA. Each day carries a median estimate and the band the model expects the flow to fall within — not a single number to plan against. Forecasts are re-issued daily; see the live screen for the current outlook.
| Date | Low p10 | Expected p50 | High p90 | Range |
|---|---|---|---|---|
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 |
All values in cubic feet per second (cfs). Estimates only — do not use them for navigation or for any safety, rescue, or emergency decision.
Typical flow by month
Long-term daily discharge percentiles from the USGS record (up to 46 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 | 2.6 | 14.6 | 274 | |
| February | 3.3 | 24.4 | 381.7 | |
| March | 5.2 | 28.1 | 364.8 | |
| April | 4 | 16.7 | 139.5 | |
| May | 0.6 | 10 | 60.1 | |
| June | 0 | 5.6 | 27.4 | |
| July | 0 | 0.8 | 10.9 | |
| August | 0 | 0 | 8.9 | |
| September | 0 | 0 | 9.5 | |
| October | 0 | 0 | 11.9 | |
| November | 0 | 1.7 | 25.2 | |
| December | 0.2 | 10.3 | 80.5 |
All values in cubic feet per second (cfs).
Common questions
- When does Santa Margarita River A Ysidora, CA normally run highest?
- March, on the long-term record. The median daily flow that month is about 28.1 cfs, against 0 cfs in August, the lowest month. These are historical normals for the date, not a forecast and not today's reading.
- What is a normal flow for Santa Margarita River A Ysidora, CA?
- It depends on the month. In January, half of days historically fall near 14.6 cfs, with the middle 80% of days between 2.6 and 274 cfs. The month-by-month table on this page gives the full range.
- How long has Santa Margarita River A Ysidora, CA been measured?
- Discharge records at USGS site 11046000 begin in 1923, about 103 years, covering roughly 9,075 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.
- Is there a flow forecast for Santa Margarita River A Ysidora, CA?
- Yes. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on this basin's observed flows, weather, and snowpack, and issues a daily flow 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 the live gauge screen. Open live conditions to see the current outlook.
- Where is Santa Margarita River A Ysidora, CA?
- The gauge sits at 33.31114, -117.34726, in California, in hydrologic subbasin 18070302, at an elevation of about 70 feet, draining roughly 723 square miles.
- Can I use Santa Margarita River A Ysidora, CA 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.