La Diagonale des Yvelines is a trail race that crosses the Yvelines department, southwest of Paris, from north to south.
Trail runner Alain Pelosse created it around 2018, building on the idea of crossing the department diagonally on foot.
Because it began with the aim of linking the west and east of Yvelines by footpath,
course passes through the Vallée de Chevreuse area, where broad farmland, valleys, forests and sandy ground alternate.
With châteaux, estates, old stables, wash houses and fountains along the way,
it is regarded not as a simple mountain trail but as a course that showcases the landscape and history of Yvelines.
The race has five categories of different lengths.
The longest, a 105km course with 1,700m of elevation gain, starts in Breuil-Bois-Robert.
The shorter 80km (from Château de Béhoust), 50km (from the Étangs de Hollande),
roughly 20km and 12km discovery course each start from a different point, but every category shares a single finish in Rochefort-en-Yvelines.
The race also awards UTMB Index points, so it is known as a course for earning an index among runners preparing for international trail series.
