Around the Grands Communaux de Trept

In Trept, take Rue des Grandes Roches. After the last houses, follow the path on the left leading to the car park, where there is a shaded picnic area with tables. This route is based on a Secirely trail. It is marked in red, but some signposts are missing. Recommended direction: clockwise. 

(S/E) Head back towards the village and turn right onto Rue des Grandes Roches until you reach the junction after the first few houses. 

(1) Turn right onto Chemin du Château d’eau. You’ll reach one of the old slate quarries, now abandoned, and continue on to Impasse de Bange, near the Route de Crémieu (D517): fromhere you can see much of the hills surrounding the town of Bourgoin-Jallieu.

(2) Turn right, then carry on straight ahead to follow the dirt track, which runs more or less parallel to the D517 and leads into a wood. On emerging from the woods, you’ll reach a junction with a view of the Saint-Hilaire Gare roundabout. This name has lost its original meaning, as the Eastern Railway Line (Lyon–Montalieu) has not carried passengers for many years and the old station is therefore disused.

(3) Continue to the right and enter the woodland again. Keep going in the same direction, ignoring the adjacent paths, until you reach a fork situated about a hundred metres from the edge of the woodland and the road leading to Le Bourg. 

(4) Turn right onto the path that climbs up to the plateau: ignore the signposting at this point. You’ll reach a crossroads at the edge of the woodland, facing the Gagne limestone quarries. 

(5) Carry straight on through heathland, skirting the quarries on your left below. You’ll reach the Pierre du Diable: the Pierre de Dieu stands on your left, about a hundred metres away. 

(6) Continue straight on to return to the car park (S/E). 

Picnic tables near the car park.

Discover a typical landscape where limestone slabs outcrop and the ‘Pierre du Bon Dieu’ and ‘Pierre du Diable’ stand tall, like strange sentinels, remnants of the Ice Age. Berry-bearing shrubs and low-growing flora, adapted to a thin layer of arid soil, thrive here. In spring, walkers come across lizards, grasshoppers and butterflies, and can spot the first lily of the valley, grasses, orchids, ferns, euphorbias and, of course, the red pasque flower – the emblem of this Sensitive Natural Area – a rare and protected plant, a wild anemone of a beautiful dark garnet colour.

Biodiversity through community action
It is a genuine collective effort centred on these communal lands that is enabling biodiversity to be restored! By designating 100 ha to the west of the village as a Sensitive Natural Area (ENS), local councillors have involved hunters (construction of hare warrens, maintenance of footpaths), naturalists from the ADPE and Lo Parvi (scientific monitoring, educational activities), a farmer (grazing, shrub clearance), quarry workers – who live near the site – and, of course, walkers.