California Region HUC 18
The California Region hydrologic region spans California, Nevada, Oregon and is divided into 126 HUC8 sub-basins. Conditions are the US Drought Monitor's weekly area coverage and the day-of-year streamflow percentiles of the USGS gauges inside each sub-basin, as of 2026-10-22.
Health score
68
Moderate
Drought index
96
Abnormally dry
Area in D2+
0.7%
1 sub-basins ≥50%
Gauges below normal
37%
of 370 reporting
Water assets
153,973
avg WIS 52.1
Sub-basins
126
42,802 alerts · 337 transfers
quality 52drought 81streamflow 67regulatory 81coverage 71
Sub-basins, driest first
| Sub-basin | Assets | Avg WIS | Drought | Gauges low | Flow pct | Health |
|---|---|---|---|---|---|---|
| Upper Klamath Lake 18010203 · OR | 398 | 49.2 | Severe (273) | 67% | p10 | 43 |
| Williamson 18010201 · OR | 328 | 55.4 | Severe (233) | 100% | p10 | 49 |
| Upper Klamath 18010206 · CA, OR | 1,595 | 64.4 | Severe (214) | 50% | p25 | 63 |
| Upper Amargosa 18090202 · CA, NV | 2,456 | 47.8 | Severe (200) | 0% | p76 | 65 |
| Lost 18010204 · CA, OR | 1,792 | 53.6 | Severe (200) | 0% | p57 | 70 |
| Scott 18010208 · CA | 1,378 | 63 | Severe (200) | 100% | p8 | 43 |
| Shasta 18010207 · CA | 669 | 56.8 | Severe (200) | 0% | p26 | 71 |
| Sprague 18010202 · OR | 641 | 56.5 | Severe (200) | 100% | p9 | 41 |
| Upper Pit 18020002 · CA | 470 | 56.1 | Severe (200) | 100% | p9 | 46 |
| Butte 18010205 · CA, OR | 372 | 49.9 | Severe (200) | — | — | 55 |
| Surprise Valley 18080001 · CA, NV | 333 | 60.2 | Severe (200) | — | — | 60 |
| Goose Lake 18020001 · CA, OR | 271 | 53 | Severe (200) | — | — | 56 |
| Madeline Plains 18080002 · CA, NV | 97 | 53.2 | Moderate (199) | — | — | 57 |
| Death Valley-Lower Amargosa 18090203 · CA, NV | 1,588 | 52.7 | Moderate (188) | — | — | 58 |
| Panamint Valley 18090204 · CA | 543 | 52.5 | Moderate (179) | — | — | 58 |
| Salmon 18010210 · CA | 1,441 | 65.1 | Moderate (171) | 100% | p20 | 56 |
| Southern Mojave 18100100 · CA | 1,889 | 45.3 | Moderate (166) | 100% | p10 | 50 |
| Lower Klamath 18010209 · CA, OR | 3,416 | 65.3 | Moderate (156) | 100% | p12 | 57 |
| Indian Wells-Searles Valleys 18090205 · CA | 1,654 | 45.2 | Moderate (155) | — | — | 57 |
| Honey-Eagle Lakes 18080003 · CA, NV | 1,160 | 49.1 | Moderate (150) | — | — | 60 |
| Salton Sea 18100204 · CA, MX | 1,029 | 43.2 | Moderate (149) | 43% | p36 | 57 |
| Smith 18010101 · CA, OR | 2,971 | 64.8 | Moderate (148) | 100% | p10 | 47 |
| Lower Pit 18020003 · CA | 613 | 55.6 | Moderate (127) | 50% | p34 | 66 |
| Sacramento Headwaters 18020005 · CA | 355 | 60.4 | Moderate (125) | 0% | p32 | 77 |
| McCloud 18020004 · CA | 236 | 62.6 | Moderate (122) | — | — | 69 |
| Mojave 18090208 · CA | 5,399 | 45.3 | Moderate (121) | 57% | p23 | 58 |
| Middle Fork Feather 18020123 · CA | 761 | 64.7 | Moderate (113) | — | — | 71 |
| Trinity 18010211 · CA | 3,838 | 65.3 | Moderate (110) | 33% | p52 | 72 |
| South Fork Kern 18030002 · CA | 418 | 66.7 | Moderate (103) | 0% | p62 | 81 |
| Coyote-Cuddeback Lakes 18090207 · CA | 1,320 | 43.7 | Moderate (102) | — | — | 62 |
| Owens Lake 18090103 · CA | 986 | 61.4 | Moderate (101) | — | — | 71 |
| East Branch North Fork Feather 18020122 · CA | 502 | 65.8 | Moderate (101) | 0% | p34 | 81 |
| Upper San Joaquin 18040006 · CA | 4,911 | 63.7 | Moderate (100) | 0% | p32 | 80 |
| Lower Eel 18010105 · CA | 3,166 | 64.5 | Moderate (100) | 67% | p20 | 68 |
| Upper King 18030010 · CA | 2,549 | 62.5 | Moderate (100) | — | — | 71 |
| Middle Fork Eel 18010104 · CA | 2,532 | 64.9 | Moderate (100) | 0% | p30 | 81 |
| Crowley Lake 18090102 · CA, NV | 2,145 | 59 | Moderate (100) | 0% | p38 | 79 |
| South Fork Trinity 18010212 · CA | 2,100 | 65.9 | Moderate (100) | 0% | p30 | 81 |
| Upper Eel 18010103 · CA | 1,723 | 63.5 | Moderate (100) | — | — | 72 |
| Mad-Redwood 18010102 · CA | 1,555 | 64 | Moderate (100) | 60% | p13 | 67 |
| South Fork Eel 18010106 · CA | 1,170 | 63 | Moderate (100) | 100% | p10 | 56 |
| Upper Yuba 18020125 · CA | 1,144 | 59.1 | Moderate (100) | 0% | p43 | 79 |
| Sacramento-Stone Corral 18020104 · CA | 1,079 | 45.1 | Moderate (100) | 100% | p19 | 54 |
| Honcut Headwaters-Lower Feather 18020159 · CA | 1,035 | 43.3 | Moderate (100) | — | — | 62 |
| Mattole 18010107 · CA | 822 | 64.8 | Moderate (100) | 50% | p21 | 66 |
| Upper Kern 18030001 · CA | 678 | 63.2 | Moderate (100) | — | — | 72 |
| Upper Cache 18020116 · CA | 652 | 56.6 | Moderate (100) | 0% | p54 | 74 |
| Upper Bear 18020126 · CA | 626 | 46.1 | Moderate (100) | 0% | p76 | 70 |
| Big Chico Creek-Sacramento River 18020157 · CA | 582 | 51.6 | Moderate (100) | 0% | p50 | 76 |
| North Fork American 18020128 · CA | 576 | 61.2 | Moderate (100) | 0% | p54 | 79 |
| South Fork American 18020129 · CA | 561 | 58.3 | Moderate (100) | — | — | 69 |
| Cottonwood Creek 18020152 · CA | 553 | 53.6 | Moderate (100) | 0% | p39 | 77 |
| Mono Lake 18090101 · CA, NV | 487 | 59.6 | Moderate (100) | — | — | 70 |
| Lower American 18020111 · CA | 484 | 44 | Moderate (100) | 0% | p39 | 73 |
| Thomes Creek-Sacramento River 18020156 · CA | 480 | 59.3 | Moderate (100) | 0% | p53 | 79 |
| Upper Stony 18020115 · CA | 469 | 63 | Moderate (100) | — | — | 72 |
| North Fork Feather 18020121 · CA | 437 | 59.9 | Moderate (100) | — | — | 70 |
| Clear Creek-Sacramento River 18020154 · CA | 432 | 51.2 | Moderate (100) | 0% | p74 | 74 |
| Butte Creek 18020158 · CA | 430 | 46.3 | Moderate (100) | 100% | p25 | 55 |
| Upper Coon-Upper Auburn 18020161 · CA | 343 | 45.3 | Moderate (100) | 0% | p32 | 74 |
| Paynes Creek-Sacramento River 18020155 · CA | 320 | 59.2 | Moderate (100) | 0% | p48 | 79 |
| Eureka-Saline Valleys 18090201 · CA, NV | 280 | 60.1 | Moderate (100) | — | — | 70 |
| Carrizo Creek 18100202 · CA, MX | 173 | 45.9 | Moderate (100) | — | — | 63 |
| Cow Creek 18020151 · CA | 126 | 55.4 | Moderate (100) | 0% | p28 | 77 |
| Battle Creek 18020153 · CA | 114 | 58.4 | Moderate (100) | 0% | p27 | 78 |
| San Felipe Creek 18100203 · CA | 244 | 47.1 | Abnormally dry (98) | — | — | 64 |
| Upper Tuolumne 18040009 · CA | 2,362 | 60.7 | Abnormally dry (96) | 31% | p58 | 71 |
| Upper Merced 18040008 · CA | 1,883 | 58.6 | Abnormally dry (96) | 100% | p13 | 59 |
| Upper Calaveras California 18040011 · CA | 251 | 45.4 | Abnormally dry (92) | — | — | 64 |
| Upper Stanislaus 18040010 · CA | 1,655 | 60.1 | Abnormally dry (88) | 50% | p23 | 70 |
| Upper Cosumnes 18040013 · CA | 373 | 45.5 | Abnormally dry (88) | 0% | p84 | 70 |
| Big-Navarro-Garcia 18010108 · CA | 1,338 | 62.3 | Abnormally dry (86) | 100% | p12 | 56 |
| Upper Tule 18030006 · CA | 1,461 | 44.9 | Abnormally dry (78) | 0% | p82 | 69 |
| Upper Mokelumne 18040012 · CA | 1,005 | 51 | Abnormally dry (76) | 100% | p10 | 58 |
| Fresno River 18040007 · CA | 1,385 | 50.1 | Abnormally dry (74) | — | — | 68 |
| San Luis Rey-Escondido 18070303 · CA | 2,594 | 42.9 | Abnormally dry (73) | 0% | p55 | 75 |
| Upper Kaweah 18030007 · CA | 2,689 | 45.5 | Abnormally dry (72) | 0% | p50 | 76 |
| Whitewater River 18100201 · CA | 789 | 44.3 | Abnormally dry (68) | 67% | p10 | 62 |
| Upper Putah 18020162 · CA | 229 | 52.8 | Abnormally dry (66) | 50% | p18 | 64 |
| Antelope-Fremont Valleys 18090206 · CA | 4,826 | 45.5 | Abnormally dry (62) | 0% | p83 | 72 |
| Lower Sacramento 18020163 · CA | 1,636 | 43.9 | Abnormally dry (62) | 50% | p29 | 65 |
| Upper Poso 18030004 · CA | 920 | 47.8 | Abnormally dry (60) | — | — | 68 |
| Rock Creek-French Camp Slough 18040051 · CA | 449 | 42.3 | Abnormally dry (59) | — | — | 65 |
| Santa Margarita 18070302 · CA | 3,041 | 43.4 | Abnormally dry (56) | 50% | p18 | 64 |
| San Diego 18070304 · CA, MX | 986 | 47.4 | Abnormally dry (49) | 50% | p30 | 64 |
| Middle Kern-Upper Tehachapi-Grapevine 18030003 · CA | 3,550 | 45.5 | Abnormally dry (45) | — | — | 68 |
| Upper Deer-Upper White 18030005 · CA | 2,584 | 43.8 | Abnormally dry (42) | 50% | p40 | 68 |
| Russian 18010110 · CA | 2,897 | 57.9 | Abnormally dry (36) | 24% | p43 | 77 |
| Middle San Joaquin-Lower Chowchilla 18040001 · CA | 5,339 | 44.7 | Abnormally dry (33) | 0% | p43 | 78 |
| Cottonwood-Tijuana 18070305 · CA, MX | 277 | 45.8 | Abnormally dry (25) | 100% | p10 | 60 |
| San Jacinto 18070202 · CA | 546 | 44.6 | Abnormally dry (21) | 33% | p88 | 67 |
| Upper Dry 18030009 · CA | 4,613 | 43 | Abnormally dry (10) | 100% | p10 | 60 |
| Aliso-San Onofre 18070301 · CA | 343 | 49.9 | Abnormally dry (9) | 0% | p100 | 70 |
| San Joaquin Delta 18040003 · CA | 1,872 | 42.1 | Abnormally dry (8) | 0% | p29 | 79 |
| Tulare Lake Bed 18030012 · CA | 4,644 | 43.5 | Abnormally dry (7) | 100% | p10 | 60 |
| Lower San Joaquin River 18040002 · CA | 1,274 | 42.2 | Abnormally dry (7) | 75% | p10 | 62 |
| Santa Ana 18070203 · CA | 2,719 | 44.3 | None (0) | 15% | p94 | 70 |
| Santa Ynez 18060010 · CA | 2,667 | 42.4 | None (0) | 64% | p10 | 65 |
| Santa Barbara Coastal 18060013 · CA | 1,877 | 42.3 | None (0) | 0% | p97 | 68 |
| Santa Maria 18060008 · CA | 1,461 | 42.7 | None (0) | 67% | p10 | 63 |
| Salinas 18060005 · CA | 1,044 | 46.5 | None (0) | 62% | p10 | 69 |
| San Gabriel 18070106 · CA | 1,019 | 44 | None (0) | 40% | p95 | 65 |
| San Pablo Bay 18050002 · CA | 973 | 46.4 | None (0) | 43% | p29 | 71 |
| San Francisco Bay 18050004 · CA | 856 | 43.6 | None (0) | 32% | p58 | 73 |
| Pajaro 18060002 · CA | 839 | 44.9 | None (0) | 50% | p22 | 71 |
| Los Angeles 18070105 · CA | 746 | 46.5 | None (0) | 20% | p52 | 73 |
| Cuyama 18060007 · CA | 636 | 47.6 | None (0) | 25% | p93 | 68 |
| San Antonio 18060009 · CA | 626 | 42.1 | None (0) | 50% | p52 | 64 |
| Central Coastal 18060006 · CA | 618 | 46.7 | None (0) | 25% | p56 | 75 |
| Gualala-Salmon 18010109 · CA | 612 | 63.8 | None (0) | 50% | p22 | 72 |
| Monterey Bay 18060015 · CA | 593 | 43.7 | None (0) | 20% | p36 | 74 |
| Santa Clara 18070102 · CA | 549 | 52.9 | None (0) | 0% | p85 | 78 |
| Seal Beach 18070201 · CA | 479 | 42.1 | None (0) | — | — | 71 |
| Coyote 18050003 · CA | 378 | 43.9 | None (0) | 17% | p44 | 77 |
| Calleguas 18070103 · CA | 372 | 45.3 | None (0) | — | — | 73 |
| Suisun Bay 18050001 · CA | 252 | 49.7 | None (0) | 100% | p10 | 63 |
| Santa Monica Bay 18070104 · CA | 227 | 46.1 | None (0) | — | — | 73 |
| Newport Bay 18070204 · CA | 199 | 43 | None (0) | 0% | p99 | 68 |
| San Francisco Coastal South 18050006 · CA | 190 | 43.1 | None (0) | 20% | p51 | 76 |
| Ventura 18070101 · CA | 117 | 51.6 | None (0) | 0% | p88 | 79 |
| Estrella 18060004 · CA | 107 | 53.1 | None (0) | — | — | 77 |
| Tomales-Drake Bays 18050005 · CA | 67 | 44 | None (0) | 0% | p58 | 77 |
| San Pedro Channel Islands 18070107 · CA | 33 | 42.2 | None (0) | — | — | 71 |
| Panoche-San Luis Reservoir 18040014 · CA | 7 | 42.4 | None (0) | — | — | 71 |
| Carrizo Plain 18060003 · CA | 2 | 43 | None (0) | — | — | 72 |
| Santa Barbara Channel Islands 18060014 · CA | 0 | — | None (0) | — | — | 100 |
Top water assets in this region
- 80Central Valley Aquifer — San Joaquin ValleyUpper Dry
- 78A Well — IrrigationLost
- 78A Well — IrrigationLost
- 78Sprs/Drainage — Primary And Supplemental IrrigationLost
- 78New Year LakeSurprise Valley
- 78Sand CreekSurprise Valley
- 76Waste Water — Primary And Supplemental IrrigationLost
- 76Drainage Ditch — IrrigationGoose Lake
- 76Sprs/Drainage — Primary And Supplemental IrrigationLost
- 76Spring Creek — AquacultureUpper Klamath