Aliso-San Onofre HUC8 18070301
A 1,597 km² sub-basin of the California region in CA. Drought coverage is from the US Drought Monitor (map of 2026-09-01); streamflow classes place each USGS gauge's latest reading against its own day-of-year record.
Health score
65
Moderate
Drought index
9
Abnormally dry
Area in D2+
0%
0% exceptional (D4)
Gauges below normal
67%
of 3 reporting
Median flow
3200%
p10 of record
Water assets
343
3 springs · 175 wells
USGS gauges (4)
- CRISTIANITOS C AB SAN MATEO C NR SAN CLEMENTE CA110463600 cfsp10 · below normal
- SAN JUAN C AT LA NOVIA ST BR AT SAN JUAN CAPIS CA110465300 cfsp10 · below normal
- ARROYO TRABUCO A SAN JUAN CAPISTRANO CA1104730022 cfsp98 · much above normal
- SAN MATEO C A SAN MATEO RD NR SAN ONOFRE CA110463250 cfsno long-term record
Recent conditions
| Date | DSCI | D2+ % | Gauges low | Flow pct |
|---|---|---|---|---|
| 2026-09-07 | 9 | 0 | 2/3 | p10 |
Top water assets
- 67Trampas Canyonreservoir
- 66Pulgas Lake Damreservoir
- 65San Mateo Creekriver
- 65Arroyo Trabucoriver
- 65Arroyo Trabuco A San Juan Capistrano Cariver
- 65San Juan Creekriver
- 65San Juan C At La Novia St Br At San Juan Capis Cariver
- 65San Onofre Creekriver
- 65San Onofre Creekriver
- 65San Mateo Creekriver