Loam
Start with the closure, then check the dirt
A land manager's closure notice settles the question. If the network is open, use Loam's condition estimate as a second check. Weather can vary over short distances, so pay attention to what you find at the trailhead too.
The short version
Check the official closure first. Read the network condition next. Turn around if the tread is soft enough to hold a rut.
A fixed rule such as "wait two days" misses too much. One network may have rocky, exposed ground while another sits under dense canopy on soil that holds water. The storm was shared. The drying time was not.
What changes the drying time
Recent rain
Amount matters, but timing does too. A small shower this morning can matter more than a larger storm several dry days ago.
Soil and rock
Fine soil can hold water near the surface. Rockier ground tends to shed it sooner, though puddles can remain in low spots.
Sun and canopy
Open slopes get more sun and wind. Shaded tread loses moisture more slowly, especially during short winter days.
Slope and drainage
Water moves off steeper ground faster. Flat sections and depressions can stay soft after the rest of a network looks ready.
A regional pattern, not a ranking
Bay Area networks sit close together on a map, but their ground is not interchangeable. Coast-facing slopes, inland hills, redwood shade, and exposed ridges respond differently to the same weather system.
That does not make one network a reliable wet-weather fallback. The safe choice still depends on its current closure status and condition. Loam scores each network from its own soil, terrain, canopy, and recent weather instead of applying one regional timer.
How to check after a storm
Open the network page
Look at the current verdict, recent rain, and the ground traits behind the estimate.
Confirm the land manager's notice
Closures and posted restrictions take priority over a modeled condition.
Check again before leaving
A passing shower can change the surface after an earlier reading.
Read the tread at the trailhead
If tires sink, leave a rut, or pick up wet soil, give the network more time.
Bay Area network conditions
These Loam pages show the latest modeled condition and any closure data available for the network.
Canopy near 64% on a 7.3° grade at 210m elevation.
Canopy near 52% on a 6.8° grade at 76m elevation.
Canopy near 67% on a 13.7° grade at 79m elevation.
Canopy near 9% on a 7.2° grade at 156m elevation.
Canopy near 82% on a 12° grade at 627m elevation.
Canopy near 65% on a 9° grade at 394m elevation.
Canopy near 5% on a 1.1° grade at 33m elevation.
Canopy near 45% on a 12.7° grade at 153m elevation.
Canopy near 36% on a 15.5° grade at 957m elevation.
Canopy near 18% on a 1.3° grade at 7m elevation.
Canopy near 62% on a 6.5° grade at 389m elevation.
Canopy near 28% on a 2.2° grade at 119m elevation.
Canopy near 83% on a 7.9° grade at 619m elevation.
Canopy near 84% on a 11.7° grade at 468m elevation.
Canopy near 49% on a 3.4° grade at 365m elevation.
Canopy near 47% on a 10° grade at 233m elevation.
Canopy near 50% on a 7.4° grade at 375m elevation.
Canopy near 56% on a 8.2° grade at 202m elevation.
The science behind the estimate
Loam starts with a simple physical fact: a trail does not dry just because the rain stops. Water has to enter the ground, move through or across the soil, and leave the trail environment. How quickly that happens depends on the soil, terrain, vegetation, recent weather, and how wet the ground already was.
Soil controls infiltration
Soils do not accept water at the same rate. USDA hydrologic soil groups range from high-infiltration soils such as deep sands and gravels to very slow-infiltration soils associated with clay, high water tables, or restrictive layers. Typical infiltration-rate ranges used in the hydrologic-group framework run from more than 0.30 in/hr for Group A to less than 0.05 in/hr for Group D when thoroughly wet.
Previous rain still matters
A storm does not start with an empty soil profile. USGS notes that soil already saturated from previous rainfall cannot absorb much more, so a larger share of the next storm becomes runoff. Recent weather therefore matters even when the latest storm was not especially large.
Terrain changes the water path
Slope changes how quickly water can move away from a surface. Low spots, drainage features, and trail geometry can change where water collects or leaves the tread. Soil classification and slope are separate pieces of the landscape, which is why both matter to a trail-condition model.
Drying is a water budget
After rainfall, water can remain in the soil, move downward or sideways, run off, or return to the atmosphere through evaporation and plant transpiration. Soil-water-balance models use these processes to estimate changing soil moisture and net infiltration over time.
Why Loam is not a rain timer
There is no useful rule that says every trail becomes rideable after the same number of dry hours. Starting moisture, infiltration behavior, terrain, canopy, and weather after the storm all change the answer.
That is the problem Loam is designed to estimate. The model combines public soil and terrain information with recent weather and network characteristics to estimate how conditions are changing. It is a model of likely trail conditions, not a sensor embedded in the dirt, and it never overrides an official closure.
What the research says
USDA and USGS hydrology work treats infiltration, soil moisture, runoff, canopy, land cover, slope, and evapotranspiration as interacting parts of the water cycle. Recent trail research adds an important piece: rainfall intensity and accumulated rainfall can strongly affect runoff and sediment generation on recreational trails, while wet conditions make trail surfaces more vulnerable to degradation.
USDA NRCS: Hydrologic Soil Groups
Soils are classified by infiltration and runoff behavior when thoroughly wet. The framework distinguishes four main groups and dual drained/undrained classes.
NRCS National Engineering Handbook →USGS: Infiltration and the Water Cycle
Explains how soil characteristics, saturation, land cover, slope, and evapotranspiration affect where precipitation goes.
USGS Water Science School →USGS: Soil-Water-Balance
A published water-budget model that estimates soil moisture, net infiltration, evapotranspiration, and canopy interception from gridded environmental data.
USGS SWB Version 2.0 →NRCS: RUSLE2
A USDA model for estimating soil loss caused by rainfall and associated overland flow, connecting rainfall and runoff to erosion risk.
USDA NRCS RUSLE2 →Fang & Ng, Journal of Environmental Management, 2026
A year-long field study found cumulative rainfall and maximum daily rainfall predicted runoff and sediment yield on recreational trails, with maximum daily rainfall the stronger predictor in that study.
Read the research →These sources describe the physical processes and research Loam draws from. They do not describe Loam's proprietary model or disclose its weights and thresholds.