Loam
Start with the closure, then check the dirt
A land manager's closure notice settles the question. Maricopa County Parks, the City of Phoenix, and Scottsdale's preserve system each post their own, and they take priority over anything else on this page. If the network is open, use Loam's condition estimate as a second check.
The short version
Check the official closure first. Read the network condition next. If a wash is running or the ground is still holding water, wait it out.
This region does not follow the same logic as a shaded, high-rainfall one. There is very little canopy to slow drying, so the ground here usually firms up fast once a storm passes. The exception is a hard monsoon downpour, which can drop more rain in an hour than a slower system drops in a day, and leave washes running well after the sky clears.
What changes the drying time here
How the rain fell
A slow winter front and a July monsoon cell can drop similar totals and behave completely differently. Monsoon storms arrive fast and hard, and intensity matters more here than the daily total.
Soil and caliche
Much of this region sits on decomposed granite over caliche, a hardpan layer that does not absorb water quickly. Rain that a looser soil would soak in can pond or run off instead, which is part of why washes rise fast during a heavy storm.
Sun and canopy
Ten of the eleven networks here measure 0% canopy. There is essentially no shade to hold moisture back, so once a storm ends, sun and wind get to work on the tread almost immediately. Papago Park is the one exception, at 17% canopy, still open by the standard of a forested region.
Slope and washes
Grade ranges from 1.4° on the flattest networks to 11.8° at South Mountain Park & Preserve. Steeper ground sheds a storm fast. Washes and low crossings are the exception: they can keep running long after the surrounding ground looks dry.
A regional pattern, not a ranking
Phoenix-area networks share the same desert climate and close to the same canopy reading, which makes this region more uniform than most Loam covers. The real spread is in grade and elevation: Brown's Ranch, at 827m, sits well above the valley floor, while Papago Park, at 377m, sits well below it.
That still does not make one network a reliable fallback after a storm. Its status depends on its current closure notice and condition on the day, and a wash crossing can hold water on an otherwise dry network. Loam scores each network from its own slope, elevation, 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 from the county, city, or preserve system take priority over a modeled condition.
Check again before leaving
A monsoon cell can build and pass through in under an hour, well after an earlier reading.
Read the wash at the trailhead
If a wash is running or the crossing looks soft, wait. A dry-looking trail can still have a wet low point.
Phoenix & Scottsdale network conditions
These Loam pages show the latest modeled condition and any closure data available for the network.
The highest network in the region (827m) and one of the steeper ones (3.7° grade), on the usual open desert ground: 0% canopy.
Zero measured canopy on a gentle 2.2° grade at 601m, typical open Sonoran desert terrain.
Tied for the flattest network in the region (1.4° grade) at 409m, with no canopy to slow drying once a storm passes.
Open desert ground (0% canopy) on a 2.9° grade at 544m, on the eastern side of the valley.
Tied for the flattest network in the region (1.4° grade) at 566m, another fully open desert network.
The only network in the region with measured canopy, 17%, and the lowest elevation (377m). Still far more open than a shaded-region network at the same reading.
A 3.8° grade over open ground (0% canopy) at 457m, close to central Phoenix.
The steepest network in the region by a wide margin (11.8° grade), at 421m, with the same 0% canopy as most of the valley. Grade, not shade, does the draining here.
A 5.2° grade at 721m, on the northern edge of the region where the desert starts climbing toward higher ground.
A 7.5° grade at 693m, among the steeper networks in the region, with no canopy to hold moisture against the slope.
A 2.3° grade at 452m on the western edge of the valley, open desert ground like most of the region.
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.