Garrotxa is a comarca (county) in Catalonia. Its population in 2001 was 47,747, more than half of them in the capital city of Olot. It is roughly equivalent to the historical comarca of Besalú.
Garrotxa borders the comarques of Ripollès, Osona, Selva, Gironès, Pla de l'Estany, Alt Empordà, and Vallespir. It includes the upper basin of the River Fluvià and the headwaters of the rivers Muga, Amer, and Llémena.
From both the human point of view and that of physical geography, the comarca has a clear division into two subcomarques. Extending north from the valley of the Fluvià, is Alta Garrotxa (Upper Garrotxa), while the southern part is sometimes called the comarca of Olot, after the capital city.
The Fluvià flows toward the Mediterranean, and has a relatively small flow of water (1.07 m3/s at Olot).
The high humidity of Garrotxa contrasts with the that of the neighboring comarques. Annual rainfall is over 1000 mm (about 40 inches). It is said that "if it's not raining in Olot, it's not raining anywhere." Winter temperatures hover around freezing; in August, temperatures average 27.7°C (about 80°F). Thermal inversions are relatively common; Alta Garrotxa and Puigsacalm, particularly, have more of a mountain climate, with snowfall figuring more prominently.
Vegetation varies with the climate. Alta Garrotxa and the east part of the comarca have typically Mediterranean climate and vegetation; the rest has a sub-Mediterranean climate, tending toward an Atlantic climate in the most humid areas.
In the western part of the comarca, the land around Olot and Santa Paucontains some 40 well-preserved volcanic cones at Croscat, important flows of basaltic lava, and the volcano of Santa Margarida. This zone is protected within the 120.07 km2 Parc Natural de la Zona Volcànica de la Garrotxa.
The principal focus is the plain and hillsides of Olot. A field of lava covers most of the plain (some 25 km2), and lava flows continue down the valley of the Fluvià to Sant Jaume de Llierca. Another important sector is in the tectonic valley of the River Ser, at the foot of the faultline escarpment of the Corb and Finestres ranges, with the volcanos of Santa Margarida and Croscat. The lava flows down the valley past the Sallent de Santa Pau to the mill of Gibert. There is a third group of volcanos in the valley of the river Llémena and the stream of Adri.
There appear to have been old eruptions around Olot, because one can find basalt boulders from the Pliocene era in the valley of the Fluvià.
In 1982, the Generalitat de Catalunya (the government of Catalonia) declared the zone comprising the valleys of the Fluvià and Ser and the upper part of the valleys of Aiguavella and Sant Iscle to be Natural Places of National Interest. They also declared most of the volcanic cones and the Fageda d'en Jordà (a beech woods rooted in lava) to be Integral Geobotanical Reserves.