The geologically old, heavily eroded range of the Westerwald is in its northern parts overlaid by a volcanic upland made of Neogene basalt layers. It covers an area of some , and therefore roughly , making the Westerwald one of Germany's biggest mountain ranges by area. In areas of subsidence, it has in its flatter western part (Lower Westerwald) the characteristics of rolling hills. Typical for the economy of the Upper Westerwald, some 40% of which is actually wooded, are traditional slate mining, clay quarrying, diabase and basalt mining, pottery and the iron ore industry, and among other things mining in the (roughly "Siegerland Ore Grounds"). Despite its relatively slight elevation, the Westerwald has for a low mountain range a typical agreeable climate. Economically and culturally, it belongs among Germany's best known mountain ranges.