Why does the western cordillera have leached soil?

Answer 1

There are five major, external factors inpacting the processes of soil formation: climate, organisms, relief (topography), parent bedrock material, time.

Here you need to look at parent bedrock and topography in hotter climates.

Leaching is done by irrigation or precipitation removing the soluble substances from the eroded particles of rock that make up the mineral content. Leaching is strongest when the bedrock mineral erodes to granular sand. This is most typical with volcanic lava rock that cooled above ground, very quickly to become crystalline. The smaller silt and clay particles that erode from magma (noncrystalline rock) are carried farthest to deposit into the valleys. This leaves the larger sand particles closest to their point of erosion making the soil very porous and prone to leaching.

Calcified soils have plenty of calcium and magnesium salts left after the acids leached away. This is because the rain that falls is more likely to evaporate than to flow through to a drainage system. This happens in inland regions of continents that dry out as playas that formed in desert valleys. The fine silt & clay minerals eroded from the mountains and deposited as shale in the valley. In wet playas leaching leaves the basic ions that cause salinaization, alkalization and calcification. Evaporation causes these soluble ions to move upwards in the layers, drawn by capillary action.