Falling rocks

What it means

This sign marks a stretch beneath unstable rock faces where stones and boulders come onto the road, either continuously in small amounts or episodically after rain, freeze-thaw cycles or blasting. Rockfall in Colorado canyon corridors ranges from gravel scattered across a lane to boulders that close the road entirely. The hazard is unusual because it can appear in seconds, without any vehicle movement contributing to it, and the debris field may sit around a curve where there is no room to manoeuvre at speed.

How it gets misread

A common misread is that the sign is historical, describing past rockfall rather than a current risk. Another is assuming visibility solves it, when rocks on the pavement are often the colour of the asphalt until you are upon them, particularly in shadow.

What to do

Drive the marked stretch at a speed from which you could stop within the distance you can actually see, and scan the pavement and the rock face together. If you see rock debris, slow well before reaching it rather than weaving at the last moment. Never stop beneath an overhang to photograph or clear your vehicle, and report fresh rockfall so the hazard is recorded.

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