Tuc de Biscarrague, Mountain summit in Briscous, France

Tuc de Biscarrague is a 91-metre summit on the border of Urt and Briscous, its top standing in Briscous above the Ardanavy valley. The summit is made of Mixe flysch, alternating clay and sandstone laid down at the Cenomanian–Albian boundary. A crescent-shaped band of older Triassic ophites lies on the southern slope.

The summit is a Cenomanian-Albian geological layer made of Mixe flysch, an alternation of clay and sandstone. On the southern slope lies a crescent-shaped band of older ophites from the Triassic to Late Triassic. The surrounding relief is later, Coniacian-Maastrichtian limestone, marly-sandy flysch and Bidart marls, so the hill stands geologically apart.

The name comes from the Gascon 'tuc', meaning height or summit, and the Basque 'bizkar' with the suffix -aga, meaning 'place of ridges'. Géoportail labels the hill Bizkarraia, while the 1:50,000 IGN map uses Tuc de Biscarrague. The summit lies in Briscous, on the border with Urt.

The summit is accessible by trails that approach from both lower elevations and nearby plateaus. Weather conditions matter significantly, as winter storms bring rain that can make routes muddy and difficult to navigate safely.

The summit's rock is Mixe flysch, alternating clay and sandstone laid down at the Cenomanian–Albian boundary. On the southern slope lies a crescent-shaped band of older ophites, rocks dating from the Triassic to Late Triassic, isolated from the surrounding Coniacian–Maastrichtian limestone and marl.