GENERAL GEOLOGIC MARK

The  space  in  which  this  small  study  is  framed  belongs  to  “La  Litera”  and  “Cinca  Medio” districts, but there are some references to the “Bajo Cinca” and “Ribagorza” too.
The  oriental  zone  of  Huesca  is  a  frontier  territory  by  geografic  position  and  by  history. Curiously, they are frontier territories with respect to their geology too, because they are in two  of  the  three  big  geologic  unities  of  which  Aragón  is  composed:  “The  Pyrinees”  and  “La depresión del Ebro”.
Of course, the zone isn ́t enclaved in “The Pyrinees”, and it isn ́t crossed by the “Ebro”. The terms used are geologic technicisms.   
The  studied  zone  presents  three  natural  unities  which  have  lithologies,  antiques,  tectonic  characteristics  and  relief,  all  of  them  brightly differentiated,  they  are  presented  as NO-SE orientation proximate strips, and they have influence in the kind of  vegetation and in the uses that have been given to the territory by its settlers.
a)
The south pyrenean hills.
They  occupy  the  north-oriental  extreme  of  the  district,  and  they  appear  in  the municipal  determinations  of  :  “Estopiñán”,  “Estaña”,  “Gabasa”,  “Calasanz”,  “Baells”,  “Nacha”, “Camporrells”, “Baldellou”, “Castillonroy”, “Santa Ana” y “Zurita”. The zone is distinguished  by  a  sequence  of  arduous  mountain  ranges  with  850  metres  heights. 
Stratigraphyly, the zone it ́s distinguished by the outcrop of the rocks which correspond to the Mesozoic and to the Inferior-Cenozoic.
The  Triasic  rocks  are  represented  by  Keuper  gypsums  which  outcrop in  the municipal determinations of “Camporrells” and “Calasanz”. The gypsums are accompained with pugs and another kinds of salt rocks as the sylvites (potashes) of “Calasanz”.
The  ofita  intrusions  in  the  rocks  of  this  period  are  frequents  too.  The  ofitas  are  subvolcanic magmatic rocks which it can be considered as dark huddles of very disturbed and scattered rocks. 
The  cretaceous  is  represented  by  limestones  and  marls,  sometimes  with  marine  fossils  of  gasteropods  and  bivalves,  and  they  are  presents  too  in  the  Garum  facies,  which are composed  by  pugs  and  sandstones  of  a  red  color  which  are  the  limit  between  the Mesozoic and Cenozoic eras and they show a period of withdrawal of the sea. 
The sedimentary series of the pyrenean side of  “La Litera” concludes whith eocene age rocks in form of big volumes of limestones with fossils, which are known as “limestone with alveolina” and can be viewed in the proximities of “Gabasa” and “Camporrells”. The alveolina  are  marine  unicellular  systems  with  millimetric  shells  of    ellipsoid  form.  This microfossils  are  accompained  by  bivalves  and  marine  gasteropods.  The  limestone  with alveolina constitutes the last marine episode of Huesca, in an age (the Eocene) in which the Pyrinees  had  already  emerged  as  a  big  mountain  range  and  in  the  South,  the  zone  of  the “Ebro”  river  was  mainland  too.  Separating  both  unities,  existed  a  marine  arm  which comunicated  the  “Cantábrico”  with  the  mediterranean  sea,  going  across  the  present  high“Litera”.
The Ebro river hollow: 
The geologic unities which belong to the Ebro river hollow are in the center, West and  South  zones.  During  the  Oligocene  (middle  of  the  Cenozoic)  the  alpine  orogeny  had conclued  in  practice  and  the  Iberian  peninsula  starts  to  have  its  present  configuration.  In the  North-East  peninsular  have  been  raised  the  “pirenaicas”,  Iberian  and  the  Coasting-Catalonian  mountain  ranges,  delimiting  a  close  basin  which  doesn ́t  have  comunication with the sea, and in which important thicknesses of sediments proceeding from the erosion of the young mountain ranges: The Ebro river hollow, are going to be accumulated during the Oligonece and the Miocene.
The Ebro river hollow beared as a continental river basin, where the sediments were conveyed and deposited by rivers and fans from the Pyrinees and the Iberian originating stratums of pugs and sandstones. In the scant wet ages, the “Ebro” river depresion would be occuped by big lakelets, being produced the sedimentation of sandstones and pugs. In the arid ages would be produced the fast evaporation of the water, being deposited then gympsums.
In “La Litera” and “Cinca Medio”outcrop rocks of the Oligocene and the Miocene, and  there  are  some  interesting  differences  with  both  rocks,  from  the  points  of  view  tectonic  and geomorfologic  evolution,  and,  so,  from  the  point  of  view  of  the  resulting landscape.
The Oligocene it ́s represented by gypsums, pugs and sandstones, and  outcrop in the zones of “La Almunia de San Juan”, “Monzón”, “Peralta”, “Azanuy”, “San Esteban”, “Tamarite”,  “Albelda”  y  “
Alcampell”.  Is  important  to  remember  that  in  this  age,  the tectonic pushes continued, so, the sediments of  The Pyrinees were compressed and folded, raising  big  folds  as  the  anticline  “Barbastro-Balaguer”  which  go  across  the  zone.  The nucleus of the anticline it ́s constituted by gypsums easily recognized because they form a kind of white wall of ONO-ESE direction in which are situated villages as “San Esteban”, “Tamarite”  y  “Alcampell”,  and  in  which  there  are  a  lot  of  folds  as  the  folds  of  the“Tamarite-Alcampell”  road.  This  gypsums  are  the  responsible  too  of  the  karstic  collapses  that  it ́s  possible  to  see  in  the  plane  of  Alcampell  as  chasms  or  small  circle  presions.  The gypsums  of  the  Oligocene  are  responsible  in  part  too  of  the  salt  character  of  the subterraean  waters  of  some  zones,    that  is  utilized  since  old  ages  to  run  commercial  that salt by salt mines, as the salt mines of “Peralta”.
In  both  sides  of  the  Anticline    “Barbastro-Balaguer”  predominate  the  sandstones  and  the  pugs  by  hard  dips.  The  fact  that  the  stratification  isn ́t  horizontal,  and  that  the sandstones  soport  better  the  erosion  than  the  pugs,  originate  peculiar  structural  leavings called slopes and hog-backs, or small asymmetric mounts in which one of the slopes is the surfaces of the stratum. The village of “Albelda” is situated in a landscape with this kind of leaving. The pendents in all the zone are softs and the figure indicating height above datum line is very rare that they are more than 500 metres. 
In the center and South of the zone are the rocks more recents of the “Ebro” river pression.  They  are  pugs  and  sandstones  of  miocene  age  and  ,  because  of  they  don ́t  have had  any  episody  of  tectonic  compression,  they  are  situated  in  horizontal  stratums.  They ocupe  the  municipal  determinations  of    “Binéfar”,  “Binaced”,  “Pueyo”, Alfantega”,  “Esplús”,  “Altorricón”,  “Algayón”  y  “Vencillón”.  This  are  the  plane  lanas  in  which  is situated  the  irrigated  of  the  “Aragón  y  Cataluña”canal  and  is  presented  as  a monotonous succession  of  big  cultured  parcels.  However,  there  are  some  interesting  leaving  of  plane roof called planes or upper millstones, and the smallest are called inselbergs. An example is the  “Sierra  de  San  Quilez”  in  Binéfar,  whose  figure  indicating  height  above  datum  line coincides with it of another tabular leaving near to the “Cinca Medio” or to “Monegros”.
The leaving of plane roof is a remembrance of the high that the zone had in the end of the Miocene, when the “Ebro” river pression was finished. Since then, and coinciding with the open  of  the  drainage  net  to  the  Mediterranean  Sea,  the  rivers  and  the  precipices  have erosioned the land, dropping some metres and doing go back the parts of tableland which are alone.
But  the  planes  of  the  South  of  “La  Litera”  and  “Cinca  Medio”  keep  another surprise.  In  the  roof  of  all  of  them  exists  a  thick  cloak  of  cemented  pebble  gravel,  of boulders,  that  have  served  of  protection  to  the  miocene  rocks  which  are  under  they  and that are decidely more soft, and so, more sensible to the erosion. The boulder cloaks are of pleistocen  age  (a  million  of  years,  more  or  less)  and  are  the  superior  terraces  and  so  the oldest of the “Cinca” river. 
The  sediments  more  recents  are  of  the  quaternary,  and  have  their  origin  in  the sedimentation  of  the  river.  They  are  in  a  big  strip  of  North-South  orientation  and  are  the plane of flood and the terraces of the river. Some of them, ocupe positions very far of the present channel, that tell us that the “Cinca” is put on the miocene rocks, but it have had a clare  displacement  to  the  west  along  the  quaternary  too.  The  rest  of  the  materials  of  this age appear as alone stains of little thick and are glacis and bottoms of precipices.