HomeNew MexicoLos Alamos County
Los Alamos County, New Mexico
Shrink-swell clay limits houses without basements on 25% of Los Alamos County's mapped land, a higher share than 75% of US counties and the 9th highest of 33 New Mexico counties. A shallow water table limits basements on 0%.
The soil survey maps 38% of the county's land area; these shares describe the mapped part. 100% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no flood losses here since 2016. 62% of homes were built before 1980, against 50% nationally; the median home dates from 1974.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Los Alamos County
| Expansive clay (limits slab homes) | 25.0% |
| High water table (limits basements) | 0.0% |
| Septic fields very limited | 64.5% |
| Clay swell (LEP, by area) | 4.7% |
| High-swell land (LEP 6%+) | 25.0% |
| Mapped soil | 26,585 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Carjo | 14% | n/a |
| Totavi | 8% | n/a |
| Hackroy | 6% | n/a |
| Frijoles | 5% | n/a |
| Calaveras | 4% | n/a |
| Cajete | 4% | n/a |
How we count · survey areas NM656 (2025-09-09)
What the numbers mean here
Clay swell averages a linear extensibility of 4.7% by land area here, and 25% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 25% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 25% of Los Alamos County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 14.29 in, 3.67 in below the 1991-2020 average year of 17.96 in.
USDA rates 65% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 52 of the last 52 weeks; the most was 100% of its area, in 52 weeks, most recently on the October 13, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 100% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Los Alamos County since 2016.
Rain
| Average year, 1991-2020 | 17.96 in |
| 12 months to August 2026 | 14.29 in (-3.67) |
| 2025 | 17.66 in (-0.30) |
| Wettest year since 1895 | 1941: 30.84 in |
| Driest year since 1895 | 1956: 6.51 in |
| Days with 1 inch or more, normal at LOS ALAMOS (1 mi away) | 1.6 |
Homes
| Housing units | 8,713 |
| Median year built | 1974 |
| Built before 1980 | 62% |
| Built 2000 or later | 19% |
| Owner-occupied | 75% |
| Median value, owner-occupied | $495,800 |
| Single-family detached | 62% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Santa Fe County, NM | 31 mi | 6% | under 1% |
| Sandoval County, NM | 35 mi | 7% | 1% |
| Rio Arriba County, NM | 49 mi | 14% | 3% |
| Bernalillo County, NM | 60 mi | 9% | under 1% |
| Taos County, NM | 61 mi | 12% | 2% |
| Mora County, NM | 78 mi | 46% | under 1% |
| Valencia County, NM | 85 mi | 4% | 3% |
| San Miguel County, NM | 89 mi | 23% | 1% |
Sources: USDA SSURGO (September 9, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status