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Morphologically, this broad tract of land, which extends from the Val d'Ainan (to the west) to the lower Guiers Valley (to the north) and Raz Mountain (to the south) is a transition between the rugged topography of the Chartreuse and the hills of the Dauphiné foreland.

Geologically, it covers, in more or less parallel strips, from east to west:

the western piedmont of the Chartreuse,

the Grand Raz secondary range belonging to the Jura and separated from the piedmont by the Miocene syncline of Voreppe,

the molassic hills, with glacial and fluivo-glacial veneers, of the Dauphiné foreland.

The valley-floor marshlands (Ainan, Morge and Guiers Mort) originated in glacial overdeeped basins filled by alluvial deposits (fluvio-glacial and fluviatile).

These valleys, the borders of Savoie until 1860, have had a turbulent history.

Economically, the Guiers Valley saw a certain prosperity due to the proximity of Chartreux, but as a whole it is part of an island where traffic moves with difficulty, which helps agricultural resist diffuse urban pressure.

* The secondary ranges belonging to the Jura are distinguished from the sub-Alpine secondary range since they link up with the Jura folds, and their stratigraphic series are different (with more reefal formations and fewer silty-clayey formations).

The Val d'Ainan includes the Saint-Julien-de-Raz plateau, the Valdaine hills and the Miribel-les-Echelles slopes, and consists of a set of smaller reliefs cut by anticlinal and other valleys, standing as an island between the Ainan Valley to the west, the Guiers Mort Valley to the north and the Western Chartreuse to the east.

The small Saint-Julien-du-Raz plateau , which culminates at the Cossert de Gilles (802m/2631ft), and the various Valdaine valleys, including one of the strongest features, the Crossey gorges, appear as small isolated worlds where woodlands and crops alternate in landscapes that call to mind those of Chambarans. There are few settlements, even though real estate pressure can be felt near Coublevie and Voreppe. The ambience so characteristic of the small romantic valley is noticeable where undergrowth and fir afforestation has been avoided, as is the case on the D28, for example, between Miribel-les-Échelles and Merlas, going over the Col des Mille Martyrs.

The slopes of the Miribel-les-Échelles hills present a landscape of mixed-farming and livestock breeding. The open continuities resulting from these activities offer magnificent views from Miribel over the Guiers Mort plain, and, vice versa, over the village itself, whose silhouette, dominated by its church, overlooks the surrounding countryside. This is a particularly strong landscape feature. This kind of situation evokes real estate pressure that needs to be controlled.

The Guiers Mort plain resembles the alluvial plains of the Dauphiné foreland, flat, and very clearly bounded by the high walls of the Chartreuse, on the one hand, and the Valdaine hills on the other. Because of its position on the Dauphiné-Savoie border, it has a turbulent, but rather prosperous history. Agriculture has developed around Saint-Laurent-du-Pont, and industry in the iron works and distillery at Fourvoirie, which was transferred to Voiron after the landslide in 1935. The famous Pont Saint-Martin , a stone arch between Dauphiné and Savoie, stands as a monumental symbol of the history of those epic times. Despite its fragility, it is still standing the test of time. It spans Guiers Vif, whose confluence with Guiers Mort is occupied by Entre-Deux-Guiers, and faces Échelles, on the Savoie right bank.