Don't ride directly after big rains.
Start in La Gouille, take the road for about 100m back to Les Haudres and take the singletrack on your right side. From this point the trail is all downhill to Les Haudres.
There is one section (about 10m) that is quite dangerous. This will be a hike-a-bike segment for most... After this descent the trail spits you back onto a dirty road.