Monsoon season in the desert Southwest: washouts, debris flows, what to check

The desert Southwest riding calendar says autumn through spring, but the transition weeks are where people get caught. Late summer is when moisture pushes up from the south and builds into afternoon thunderstorms that drop a great deal of water onto ground that cannot absorb it. The result is not a wet trail. It is a trail that has moved.

A wash that was a smooth sandy road in April can carry a wall of water and rock for a few minutes and then be dry again by evening, with the crossing gone and a cutbank where the ramp used to be. Ocotillo Wells SVRA in California is largely sand and washes, and its managers at California State Parks note the park stays open in summer while heat is extreme. Open does not mean unchanged.

Johnson Valley OHV Area is the same story on a larger scale. The dry lakebeds go from hard pan to something like wet concrete after a storm, and the desert two-track between the rock trails crosses dozens of drainages. The BLM Barstow Field Office also closes the shared-use area during scheduled military training windows, so there are two separate reasons to check before driving out there and neither of them is the weather forecast alone.

Logandale Trails in Nevada is restricted to designated routes across red sandstone and sand, and storm damage here tends to show up as routes that are cut or blocked rather than reshaped. The BLM Southern Nevada District Office notes summer heat near Overton as punishing; add that a designated route may be impassable after a storm and you have a good argument for waiting a few weeks.

Moab and Sand Hollow sit at the Utah end of the same weather. Slickrock sheds water quickly, which is exactly the problem: the runoff concentrates in the sandy drainages between fins and can leave deep, soft trenches where a firm approach used to be. Sand Hollow's sandstone trails such as The Maze are less affected than its dunes, but the park entrance road and staging areas are worth asking about.

The practical rule for anyone riding the desert in this window is to be off exposed ground and out of washes by early afternoon. Flash flooding does not require rain where you are standing; a storm many miles upstream can send water down a dry channel under a clear sky. If you can hear it, you are already late.

Agencies do post closure notices after significant storm damage, but they do not inspect every mile of two-track, and a route that is officially open can still have a missing crossing. Confirm with the managing agency before you go, and then treat the first miles as a scouting run rather than a drive.

On the machine side, water crossings that were not there last time are a reason to check what the site's maintenance guidance already flags: brake pads, grease in the joints, and differential fluid on trucks and SUVs, which can be contaminated by a crossing without any outward sign. The intervals and values are in your service manual.