The oldest rock in the study area corresponds to the lower Cretaceous Metamorphic (schists). Above these metamorphic rocks are clayey limestones and Shales of the Cretaceous Soyatal Formation. The sedimentary rocks of the Cretaceous are covered by (ignimbrites and rhyolites) felsic volcanic rocks of the oligocene-miocene

reaching thicknesses of 600 m. Since the Valley is of tectonic origin, collapsed, volcanic rocks are covered by continental deposits (sandstones and conglomerates) with a thickness of 300 m. The last volcanic activity (basalts) occurred during the Quaternary. Finally, Quaternary clayey deposits cover the Valley, reaching 150 m thick (Figure 3).

The vertical forces that cause fracturing the rock are due to the internal movements of the Earth’s crust which in turn cause deformation, cracks and faulting in the rock.

The structural geology of Celaya Valley lies within what is known as the Neovolcanic axis, reason why there are numerous faults in this area. The study area is affected by various systems of faulting, one belonging to the system Taxco-San Miguel de Allende orientation NNW-SSE [6], which passes through the center of Mexico, another fault with orientation system E-W is associated with the Transmexican Volcanic Belt. Normal type faults are reported in the study area (Figure 3(b)), similar to the system oriented Taxco-San Miguel.

In the city of Celaya at the end of the 70’s, were appreciated for the first time cracks and subsidence affecting urban infrastructure, mainly, was in these years that a study was begun to determine the cause of the cracking, within the results, it was determined that in the city the largest differential movement was 60 cm, currently the displacement is 3.5 m, these normal faults remain active and glide at a speed of 15 cm a year.

There are six normal faults that have records: 1) Fault

Pradera de la Hacienda, 2) Failure La Corona, 3) Gobernadores fault, 4) Fault Universidad Pedagógica, 5) Fault Insurgentes and 6) Mercado de Abastos fault, these six mentioned are only visible within the urban area, the continuation that have these faults to the North and South of the city, on the agricultural zone is evident, however, because the soil is removed constantly affected agricultural land leveling, you can not specify a rate of displacement.

Celaya Valley aquifer is one of the largest aquifers that exist in the State of Guanajuato because of its number of wells. The oldest well reported in the Valley of Celaya is known as Bola de Agua was one of the first wells drilled in the year of 1910, to supply the population of Celaya, when this well was drilled the water raised 2 m above the ground level. By the year of 2009 the depth of the static level reached 110 m [3]. The density of wells was growing over the years, only to 1970 there were approximately 1032 wells, by the year of 1990 reported a total of 1897 wells (Figure 4) of which the 0.26% were abandoned, the 0.42% were used for watering holes, the 94.80% for agricultural use, the 2.37% were for household use and finally the 2.11% were used in drinking water for the city [7], in 1999, surveyed 2162 wells, and the 1.99% were abandoned, the 1.06% were used even as a watering hole, the 84.18% were for agriculture irrigation, 2.08% were to domestic use, the 7.59% were for drinking water, the 2.59% of the wells were used for the industry and finally the 0.51% of the wells were used for

recreational use [8]. The National Commission of Water (CNA), in 2003 reported the existence of 2948 wells and only 2441 were active; they were classified in three categories, agriculture with a total of 1830, public supplying 540 and industrial with 71 wells.

With regard to the lifting of the static level, in the year of 1956, there were so many alterations to the aquifer and the number of wells did not exceed 100 (Figure 4). Agricultural activity and the development of the aquifer were located mainly in the central part of the Valley and another area where there was this same development was to the West of the city of Celaya. The extraction of groundwater in the Valley initiated the formation of a small drawdown elongated of orientation NW to SE. Figure 5 shows to the northeast of the study area, high piezometric of 1760 meters above sea level (MASL), indicating an important recharge area (Figure 5(a)).

Census of 1990, the CEASG reports 1897 wells in the

Valley of Celaya. The piezometry shows a greater extension of the drawdown that reaches the city of Celaya (Figure 5(b)), with a low piezometric level (1678.45 MASL) and in addition, a general decrease of the Valley piezometric levels.

With an increase in a period of eight years, the number of wells increased to 2162 on the year 1998, the drawdown defined towards the center of the Valley, taking an elongated form with directions NW-SE which passes through the city of Celaya (Figure 5(c)).

In the 2000 census, the number of wells had no significant variations and the drawdown displayed a recovery of its levels towards Celaya; however, towards Villagran, the drawdown had significant declines (Figure 5(d)).