Mission and methods
Or: the beta behind the beta.
The mission: save the holds
Wet sandstone breaks. Pull on a soaked crimp and it can snap off in your hand, and that hold is gone for every climber after you. The route you were psyched on just got harder, or it's chossy forever. Can You Send is a free, volunteer-built tool that gives you the call in one glance: has the sandstone at 61 US crags likely had time to dry? If not, it points you to nearby rock that shrugs off rain, so you can still get your pitches in. The goal: protect the routes, keep climbers safe, and get you sending on the right day.
How the call is made (the beta)
- Rain gauges: the eyes on the crag. Every hour the site pulls rain totals from up to 5 automated gauges within about 10 miles of each crag (closer where gauges are dense). A gauge that's gone quiet for 6 h gets benched. If none are reporting, the site falls back to gauges 15 to 20 miles out, then to a weather-model estimate, and the page tells you so.
- Measurable rain. Rain counts at 0.01 inch or more, the standard threshold for measurable precipitation. It takes 0.10 inch or more at a gauge inside the wet window to call the rock likely wet; anything less is a trace, which means caution.
- Drying model: how long until it goes. The site takes the most recent rain event at the gauges near the crag (showers within 6 hours count as one, and rain on rock that's still damp stacks on top). The amount sets how much drying the rock needs, in hours of good drying weather: about 4 h for a trace, 12 h for 0.05 inch, 24 h for 0.10 inch, 48 h for half an inch and 72 h for an inch (the hard sandstone of the East needs three quarters of that). Then, hour by hour, the National Weather Service forecast's humidity, temperature, wind and cloud cover, plus the sun's height by time and season, set how fast it dries. That's the Penman evaporation equation in climber terms: sun on the rock plus wind times how thirsty the air is. A clear, dry autumn desert day counts as about 24 hours of drying; a cool, humid, cloudy one, only a few. "Likely climbable by" is when the drying adds up, and the page stays at caution a little longer for shady faces.
- Forecast: what's coming over the ridge. The National Weather Service hourly forecast for the next 12 h gets checked. A 30% rain chance or more means caution (at 60% or more the page says rain is likely). A forecast alone never calls the rock wet: that takes a gauge measuring real rain.
- Worst reading wins. 🟢 Likely dry only when every gauge and the forecast agree. One gauge or one forecast hour can flip it to 🟡 yellow or 🔴 red, and every reason is listed on the area page, so you can read the beta yourself.
| Rock group | 🔴 Likely wet for | 🟡 Caution until | 🟡 Winter caution |
|---|---|---|---|
| Fragile when wet (32 areas) | 48 h | 72 h | 96 h |
| Hard sandstone (29 areas) | 24 h | 48 h | 72 h |
Hours after the last measurable rain. These windows are the starting rules; once the drying model says the rock has dried, it relaxes them, and when no forecast weather is available they apply as they are.
Why rock type matters
Sandstone is sand grains glued together by a natural cement of clay, calcite, iron oxide or silica. It's porous, so rain soaks in like a sponge. Water softens clay and dissolves weak cements, and the grains let go: wet sandstone can lose up to 75% of its strength (Southern Nevada Climbers Coalition, Access Fund). That bomber jug might not be bomber.
- Not all sandstone is equal. Lab tests on 35 sandstones found strength losses from 8% to 78% when saturated, depending mainly on how much quartz and clay the rock holds (Hawkins & McConnell, 1992).
- A little water matters. Rock strength drops noticeably at only about 1% water saturation, so "mostly dry" isn't dry (Vásárhelyi & Ván, 2006).
- Fragile when wet is the soft, porous, weakly cemented sandstone of the West (Aztec, Navajo, Wingate, Dakota and similar), plus any area whose rock strength we couldn't confirm. These get the longest windows, matching local guidance like the SNCC's "at least 24 hours, 3 to 4 days in winter" and Zion's two-day rule (NPS Zion).
- Hard sandstone is the quartz-rich, well-cemented stone of the East and Midwest. The New River Gorge's Nuttall is a silica-cemented, nearly pure quartz sandstone (NPS New River Gorge, West Virginia Encyclopedia), and the Red River Gorge's Corbin is a similar quartz sandstone. Rock like this loses the least strength when wet, so the windows are shorter, but soaked holds still need time.
- Rainy-day crags (limestone, granite, basalt and similar) are dense, with little pore space, so rain mostly stays on the surface and the rock dries fast. They're not bulletproof: soaked limestone loses strength in lab tests too (EPFL, 2024), but in practice holds don't crumble the way soft sandstone does, so locals head there on wet days.
Fragile when wet: Red Rock (Aztec Sandstone), Indian Creek (Wingate Sandstone), Zion (Navajo Sandstone), Joe's Valley (Sandstone), Garden of the Gods (Lyons Sandstone), Castlewood (Conglomerate sandstone), Castle Rock (Vaqueros Sandstone), Stoney Point (Sandstone), St. George (Navajo Sandstone), Moab (Wingate and Navajo sandstone), Capitol Reef (Wingate Sandstone), Sedona (Soft sandstone), Valley of Fire (Aztec Sandstone), Mentmore (Gallup Sandstone), Colorado NM (Wingate Sandstone), Horsetooth (Dakota Sandstone), Morrison (Arkose sandstone), Durango (Dakota Sandstone), Santa Barbara (Sandstone), Mt. Diablo (Sandstone), Larrabee (Chuckanut sandstone), the Rims (Eagle Sandstone), the Callahans (Tyee Sandstone), Sespe Gorge (Sandstone), Rock City (Dakota Sandstone concretions), Banning (Kettle River sandstone), El Rito (Cobble conglomerate), the Swell (Wingate and Navajo sandstone), Sinks Canyon (Tensleep Sandstone), Mineral Wells (Sandstone conglomerate), Robinson Park (Kettle River sandstone), Grand Ledge (Soft sandstone).
Hard sandstone: the Red (Corbin Sandstone), the New (Nuttall Sandstone), Eldo (Fountain and Lyons sandstone), Flagstaff (Fountain sandstone), Peshastin (Silica-cemented sandstone), Palisades (Sandstone), Cowell (Sandstone), Denny Cove (Sandstone), Castle Rock TN (Sandstone), Sunset Rock (Sandstone), the Meadow (Nuttall Sandstone), Robbers Cave (Bluejacket Sandstone), HCR (Sandstone), Sam's Throne (Sandstone), Crystal Bluff (Jackfork Sandstone (hard, quartzitic)), Jackson Falls (Sandstone), Giant City (Sandstone), Whipp's Ledges (Sharon Conglomerate), T-Wall (Sandstone), Stone Fort (Sandstone), Foster Falls (Sandstone), the Obed (Sandstone), Rocktown (Coarse sandstone), HP40 (Sandstone), Moss Rock (Sandstone), Little River (Sandstone), Sand Rock (Sandstone), Summersville (Nuttall Sandstone), Coopers Rock (Sandstone).
Sources: where the beta comes from
- Synoptic Data and MesoWest (University of Utah): rain gauges, current wind and temperature from public and private weather networks.
- Clark County Regional Flood Control District: its rain gauge network around Las Vegas, for the Clark County crags (Red Rock, Valley of Fire).
- Oklahoma Mesonet and Kansas Mesonet: research weather stations near Robbers Cave and Rock City.
- CoCoRaHS: daily rain reports from volunteer observers near the crags. Thank you, gauge readers.
- National Weather Service API and NWS forecast: hourly rain chance, rain amounts, wind and temperature for each crag's forecast grid cell, with the NWS forecast linked on each page.
- Open-Meteo: weather-model rain estimates when no gauge is reporting.
- Mountain Project: crag locations and area pages.
- Access Fund and the local climbing coalitions credited on each area page: wet-rock ethics and access.
- Wet Rock Police (Grant Mercer and contributors): the original "has it rained at the crag?" site. Big respect.
- Land managers (NPS, BLM, US Forest Service, state and city parks): closures, permits and wet-rock rules, linked on each area page.
- Llama Guard 3 on Cloudflare Workers AI: screens Local Beta Board posts.
- Science: Hawkins & McConnell (1992), Vásárhelyi & Ván (2006), water weakening of carbonates (EPFL).
Limits: don't trust it like a bolt
- Gauges measure rain, not rock. A storm can miss the gauge and hit the crag, or the reverse.
- Drying varies wall by wall. Sun, wind and aspect speed it up; shade, seeps and humidity slow it down. The windows are conservative averages, not a promise. Treat the call like guidebook grades: useful, sometimes a sandbag.
- Snow is tricky: many gauges under-measure it, and melting snow can keep rock wet for days after the last storm.
- Always check the rock and the ground yourself. See how it works and the terms.
Spotted an error, or got better beta for your area? Email canwesendit@gmail.com.
Last updated November 2, 2026. Questions: canwesendit@gmail.com. Follow Can You Send on Facebook ↗