USGS Streamgage 11303500
San Joaquin River near Vernalis, CA
San Joaquin River near Vernalis, CA is USGS streamgage 11303500 in California, monitoring river discharge in hydrologic subbasin 18040003. It drains a watershed of about 13,539 square miles. Discharge records at this site go back to 1923. Typical flow runs near 1,289.7 cfs in July and 2,959.7 cfs in April, with the higher of the two arriving in April.
Gauge details
- State
- California
- Drainage area
- 13,539 sq mi
- Gauge elevation
- 3 ft
- Subbasin (HUC-8)
- 18040003
- Coordinates
- 37.67601, -121.26629
- USGS site number
- 11303500
- Records begin
- 1923-10-01 (103 years)
Typical flow by month
Long-term daily discharge percentiles from the USGS record (up to 103 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 | 1,138.1 | 2,598.7 | 11,351.6 | |
| February | 1,213.7 | 3,274.8 | 16,034.5 | |
| March | 980.8 | 3,334.2 | 19,393.5 | |
| April | 810 | 2,959.7 | 21,553.3 | |
| May | 739 | 3,296.5 | 21,835.5 | |
| June | 541.4 | 2,482.3 | 17,606.7 | |
| July | 357.6 | 1,289.7 | 6,659.4 | |
| August | 360.6 | 1,088.7 | 3,117.1 | |
| September | 434.5 | 1,282.3 | 3,208.3 | |
| October | 800.1 | 1,821 | 3,795.2 | |
| November | 975.1 | 1,735.3 | 3,441 | |
| December | 976.5 | 2,055.5 | 5,455.2 |
All values in cubic feet per second (cfs).
Common questions
- When does San Joaquin River near Vernalis, CA normally run highest?
- March, on the long-term record. The median daily flow that month is about 3,334.2 cfs, against 1,088.7 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 San Joaquin River near Vernalis, CA?
- It depends on the month. In January, half of days historically fall near 2,598.7 cfs, with the middle 80% of days between 1,138.1 and 11,351.6 cfs. The month-by-month table on this page gives the full range.
- How long has San Joaquin River near Vernalis, CA been measured?
- Discharge records at USGS site 11303500 begin in 1923, about 103 years, covering roughly 9,126 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.
- Where is San Joaquin River near Vernalis, CA?
- The gauge sits at 37.67601, -121.26629, in California, in hydrologic subbasin 18040003, at an elevation of about 3 feet, draining roughly 13,539 square miles.
- Can I use San Joaquin River near Vernalis, 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.