Western Peninsula Geology: Granite, Limestone and Shale Landscapes

Siliceous Area

Area silícea: Ancient and primary rocks located in the western part of the peninsula. This area shows little branching to the west. The predominant rock is granite.

Types and processes: In some cases the granite is chemically altered at depth by water. In other cases the granite is altered along fractures that are perpendicular to the strata, forming boulders and blocky accumulations (berrocal) that pile up. When these blocks become unstable and are displaced, they produce areas of granitic chaos.

Limestone Area

Limestone Area: Rocks of secondary origin, located in a Z-shaped, inverted zone of the peninsula. The predominant rock is limestone. Karst processes generate characteristic relief forms:

• Sinkholes: Depressions or hollows in the surface.
• Gorges (gargantas): Narrow, steep-sided valleys carved by rivers.
• Valleys: Narrow and deep valleys caused by fluvial erosion.
• Poljes: Elongated depressions framed by steep slopes.
• Dolines: Large cavities formed where water accumulates and stagnates.
• Caves: Subterranean galleries excavated as water infiltrates through cracks in the limestone.
• Chasms: Narrow openings that connect the surface with underground galleries.

Shale Area

Shale Area: Rocks of Tertiary and Quaternary age. Watersheds are located on sub-plateaus to the north and south. In the depressions the dominant fluvial system is the Guadalquivir. The rocks include deposits associated with the Ebro basin and extensive clays, producing predominantly horizontal relief.

Types and forms: Campiñas (gently undulating plains) where rivers flow and form gullies. The gullies are narrow, deep grooves separated by ridges.

Apalaxense Relief

Apalaxense Relief: A Hercynian mountain relief that was heavily eroded; subsequent uplift and renewed erosion created a reactivated landscape characterized by alternating peaks and valleys.

Geographical Climate

Latitude and Seasons

Latitude: Located in the Northern Hemisphere temperate zone, which determines the existence of well-defined seasons: summer and winter, with transitional seasons (spring and autumn) in between. In the Canary Islands, due to latitude, the seasonal contrasts are smaller.

Geographic Situation

Situation: Located between large bodies of water and between two continents, which makes the area a crossroads for different air masses.

Marine Influence

Influence of the sea: Low in much of the interior because of the large continental width and the limited penetration of maritime effects, compounded by mountain ranges that run parallel to the coast and act as barriers.

Relief and Temperature

The relief: The position of most mountain ranges hinders the passage of air masses. Temperatures decrease with elevation — approximately 0.5 °C per 100 m of ascent. Each slope orientation (aspect) causes climatic contrasts between sunny (exposed) and shady slopes.