The Sierra Gorda (lit. 'fat mountain(s)') is an ecological region centered on the northern third of the Mexican state of Querétaro and extending into the neighboring states of Guanajuato, Hidalgo and San Luis Potosí. Within Querétaro, the ecosystem extends from the center of the state starting in parts of San Joaquín and Cadereyta de Montes municipalities and covering all of the municipalities of Peñamiller, Pinal de Amoles, Jalpan de Serra, Landa de Matamoros and Arroyo Seco, for a total of 250 km² of territory. The area is extremely rugged with high steep mountains and deep canyons. As part of the Huasteca Karst, it also contains many formations due to erosion of limestone, especially pit caves known locally as sótanos. The area is valued for its very wide diversity of plant and animal life, which is due to the various microenvironments created by the ruggedness of the terrain and wide variation in rainfall. This is due to the mountains’ blocking of moisture coming in from the Gulf of Mexico, which generally makes the east side fairly moist and the west semiarid scrub brush. Most of the region is protected in two biosphere reserves, with the one centered in Querétaro established in 1997 and the one centered in Guanajuato established in 2007. The Sierra Gorda is considered to be the far west of the La Huasteca region culturally and it is home to the Franciscan Missions in the Sierra Gorda of Querétaro World Heritage Site. Sierra Gorda has become the first National Park in Mexico to join the EarthCheck Sustainable Destinations program.

The region is on a branch of the Sierra Madre Oriental mountain range and consists of a series of mountain chains that run northwest to southeast, formed 240 million years ago. Most are made of limestone, formed by sea beds from the Jurassic and Cretaceous periods. Later there were intrusions of volcanic rock, especially in the eastern portion in Hidalgo state, from which come the mineral deposits of the area. The limestone has been affected by erosion to form the Huasteca Karst, and the area contains a large number of caverns, and pit caves (sótanos), some of which extend for hundreds of meters in depth. All of the Sierra Gorda is marked by very rugged terrain, which includes canyons and steep mountains. Elevations range from just 300 meters above sea level in the Río Santa María Canyon in Jalpan to 3,100 m asl at the Cerro de la Pingüica in Pinal de Amoles. The most significant peak in the Hidalgo area is Cerro Cangandhó which has an elevation of 2,820 m asl. Rainfall also varies greatly from 350 mm to 2,000 mm per year. Among its mountains are the peaks associated with the Sierra Alta de Hidalgo, the pine forests of Zamoarano, the Extoraz Canyon and the slopes of the Huazmazonta, the inter-mountain valleys where the five missions are found and the rolling hills leading into La Huasteca. The wide variations of elevation and rainfall favor a wide variety of flora and wildlife.

There are three main rivers in the Sierra Gorda, all of which are part of the Pánuco River basin. These are the Santa María River, the Extoraz or Peñamiller River and the Moctezuma River. All three pass through deep canyons and tend to form borders between the states and municipalities of the region. Santa María marks part of the border between Querétaro and San Luis Potosí, and the Moctezuma River marks part of the border between Querétaro and Hidalgo. The Tula and Moctezuma Rivers meet in the Sierra Gorda of Hidalgo. Here, the Moctezuma River Canyon extends for twelve km and rises 480 meters above the floor.

The climate of the region depends on elevation and that the mountains form a natural barrier against the main source of moisture, the Gulf of Mexico. The east side of the mountains gets significant more rainfall than the west, in the form of orographic precipitation and clouds as the moisture-laden winds from the Gulf of Mexico ascend the mountain slopes. Forests and even rainforests are found in the east, while the west is dominated by desert and near desert conditions. In the east, mornings in the high mountain areas usually bring cloud cover and fog. The most moisture falls in the northeastern edges of the regions, where it merges into La Huasteca proper, in San Luis Potosí and Hidalgo. In the entire region, the coldest temperatures occur between December and January, with high temperatures in April and May. Temperatures vary widely depending on elevation with an annual average of 13 °C in the higher elevations such as Pinal de Amoles to 24 °C in lower areas such as Jalpan. In the highest elevations, frosts and freezes are not uncommon. In 2010, the Sierra Gorda had it first significant snowfall in eighteen years in the municipality of Pinal de Amoles, with temperatures of −4 °C. In some places, the cover was 15 cm deep.

Because of its great variety of ecosystems, the Sierra Gorda has one of the diverse ecologies in Mexico, with one of the largest number of species of plants and animals.

The micro-environments of the region range from conifer forests, oak forests, mostly found on mountain peaks, banana and sugar cane fields in the deeper canyons. On the east side, there are deciduous forests. On the west side, bordering the Mexican Plateau, there are desert and semi desert conditions, with a variety of cacti and arid scrub brush.

Species in danger of extinction include the jaguar, puma, the black bear, the green parrot, the Veracruz partridge, and the Humboldt butterfly, mostly due to human activities. Endangered plant species include the biznaga gigante (Echinocactus platyacanthus), the chapote (Diospyros riojae), the guayamé (Abies guatemalensis), the magnolia (Magnolia dealbata) and the peyote (Lophophora diffusa). monarch butterflies can be found in the area as well, as they pass through to their wintering grounds on the State of Mexico-Michoacán border . There have been plagues in the forests of the area due to the recent drought conditions. The most serious is a bark beetle (Dendroctonus adjunctus) and mistletoe (Arceuthobium sp.). The drought conditions have been blamed on global climate change. Areas in Querétaro and Guanajuato have been declared as biosphere reserves. The Sierra Gorda in Hidalgo has not, but it still contains a large number of important ecosystems.

There are two major conservation areas in the Sierra Gorda region: one in Querétaro and one in the state of Guanajuato.