Sichuan has a vast land with diverse soils. It can be roughly divided into three major soil zones: eastern Sichuan basin humid forest soil zone, southwestern Sichuan mountain valley forest soil zone and western Sichuan mountain plateau subhumid semi-arid forest and alpine meadow soil zone. In the eastern basin, there are continuous hills; the outcrop is mainly Jurassic and Cretaceous purple sandstone and mudstone, which have developed into purple soil and thereby into the well-known “Red Basin”. Except some parent materials in the Cretaceous Guankou formation and Jiaguan formation in southwestern and southern Sichuan react acid, the remaining majority of parent materials react neutral or basic. In eastern basin, between the Quhe River and the Yangtze River is a group of parallel ridge-valleys taking on a northeast-southwest strike; the outcrop on the mountains is mostly thick sandstone of Triassic Xujiahe formation and Triassic and Permian limestone, which have developed into yellow soil. In the Western Sichuan Plain, there is a large area of moisture soil distributed in a concentrated way. The peri-basin mountain soil has an obvious vertical distribution feature, that is, yellow soil, brown yellow soil, brown soil, dark brown soil, brown coniferous forest soil, from bottom to top. In southwestern Sichuan, there is a huge height difference between the mountains and the valleys; the vertical distribution spectrum of soil is dry red soil, red soil, red brown soil, dark brown soil, brown coniferous forest soil and mountain meadow soil. On the surfaces of western mountains and plateaus are mainly mountain meadow soil, subalpine meadow soil, alpine meadow soil and patchy swamp soil; on the lofty ranges is alpine cold desert soil. Below the plateau surface are mainly gray cinnamon forest soil, cinnamon soil, brown soil, dark brown soil, brown forest soil and subalpine meadow soil.
1. The soil-forming rock in Sichuan karst regions is mainly limestone, dolomitic limestone, limestone mixed with aleuvite, conglomerate, etc. There are abundant types of soil. The relatively pure carbonate rock contains little insoluble moisture and slowly weathers to soil. In the karst regions, due to the thin soil layer, loose soil, many gravels and low adhesive force between rocks and soil, the soil not protected by vegetation can be easily eroded and thus become infertile. In the karst regions, there are mainly four soil subgroups: yellow limestone soil, brown limestone soil, red limestone soil and black limestone soil; due to the impact of development degree and eluviation, there is also some mountain yellow soil.
2. In the northwestern Sichuan plateau region, there are mainly alpine meadow soil, subalpine meadow soil, swamp soil and alpine cold desert soil. There is aeolian sandy soil in Zoigê, Hongyuan, Aba and other county-level regions. Due to the special geographical environment, the horizontal distribution features of soil in the northwestern Sichuan mountain-gorge region have been destroyed and some new types of soil are developing, such as mountain gray cinnamon forest soil, mountain cinnamon soil, moisture soil and new accumulative soil.