The present study was conducted in the county of Jaguariúna (Experimental Field of the Embrapa, Environment), to understand the recent evolution of the slope adjacent to headwaters. A representative soil transect was studied through borehole and trenches, of the top up to the drainage axis, with the objective of reconstituting of the organization of the pedologic covering. It was verified that, starting from the inferior third part of the slope, it exists, inside of the latossolic covering, a hidromorphic horizon. This horizon has the same morphology of the current water magazine located in the base of the pedologic covering. These two hidromorfics groups are separated through a latossolic material that disappears when these two groups reach each other. In the basis of the slope, above the alteration material with facies of water magazine, there is a peat, with up to 1,5m of thickness, dated, through 14C, of 31250 + / - 250 years AP. Covering it there is a colluvium.
We have hypothesized that the horizon with morphology of water magazine constitutes a relic of an old magazine from a period when the pedologic covering was in higher level than the current. The understanding of the several phases of evolution will distinguish the following episodes in the considered period (of unknown maximum age):
- - An initial phase in that a latossolic covering existed with suspended water table,
- - An incision phase due to a fast lowering of the base level,
- - A phase of stability of the base level when the drainage axis presented a wetland morphology in which was formed the peat.
- - The current phase when the slope was rectified by erosion to amount and colluvial deposits at the downstream. The valley acquires morphology in open V, with slopes lightly convex-concave.