Gran Dolina is one of the archeological sites at Sierra de Atapuerca (the most important one actually). A whole new species of man was discovered here (Homo antecessor). The findings at Gran Dolina have invalidated several previous beliefs about European prehistory.
Gran Dolina is a cave, a rather large one actually. It is about 20 meters deep, but the width is uncertain because of a cave-in thousands of years ago. This cave is open to the air and is part of the diaclasas system that crosses the Sierra de Atapuerca. This cave along with others in the vicinity was a longterm home to many of the prehistoric humans in the area. This site has been undergoing excavation since 1984.
The archeologists that are excavating the Gran Dolina have divided it into 11 sedimentary levels (TD1 - TD11), dating from the Lower Pleistocene all the way to the Late Pleistocene era. (The lower the number, the older the level). Most of the really important fossils have been found at the TD6 level (the Homo antecessor fossils). Only the two upper levels (TD11 and TD10) have been fully excavated, the rest of the levels have only really had a few "test digs" done on them.
TD4, TD6, TD10, and TD11 are the only levels of any real importance, so those are the ones that I am going to elaborate on. The others have yielded little of any real importance. (I better explain the whole "level" thing a little better, in case you have no clue what I am talking about). Some caves will actually fill up over time, little bits of dirt and rocks will collect to slowly (over thousands of years), raise the floor of the cave. By digging, you can discover things from an earlier time period. It works this way outdoors also. This is why you don't find fossils just lying around on the ground (well not usually at least).
This is the oldest level that has any significance (close to a million years old). Several herbivore fossils were found. Along with four quartzite tools. Evidence shows that several hominids made a few tools in the cave, most likely to easily cut up some of the animals that may have fallen into the cave (it was deep at this point in time). The cave was not regularly occupied at this time however. As indicated by a lack of any hominid fossils or major lithic activity at this level.
This is the most important level to date (about 800,000 years old, and this is where the Homo antecessor fossils were discovered). The Gran Dolina was heavily occupied during TD6 (and almost continually afterwards). The inhabitants at this level were great hunters, as indicated by many herbivore fossils with cut marks and broken bones (but with no teeth marks from carnivores). Remains of at least 6 of hominids of the Homo antecessor variety were found to have the same cut marks as the herbivores (early cannibalism perhaps).
The TD6 inhabitants left behind a number of primitive tools made of flint, quartzite, sandstone and limestone. Along with with the waste that shows the tools were produced there. These tools used only primitive knapping methods, and no advanced tools were found. The technological level is similar to that of the earliest discovered African tools. Further analysis has shown that the main functions of these tools was in dismembering dead animals.
The findings at TD6 have invalidated previous theories that had put the earliest occupation of Europe at 500,000 years ago. It is now believed that Europe was occupied at least 1 million years ago (perhaps even earlier).
TD10 is around 150,000 years old. This level shows the same intense occupation as TD6. Along with a great increase in the toolmaking technology (hafted tools made with more advanced knapping techniques were discovered). The first evidence of skin processing was also discovered at this level (skin processing means the curing or altering of animal skins for other uses). The skins were mainly from the horses and deer that were the staple of the occupants diets.
The cave began to collapse at this level. That combined with the fact that the cavern was only 2 meters tall at its highest at this point (remember, sediments raise the cave floor), signalled the end of human occupation of the Gran Dolina. It is thought that activities where moved to another nearby cave (which is still undiscovered).
The Gran Dolina is still being excavated today. There is no doubt that it still has a wealth of information to offer on prehistoric man. For more information, please take a look at the websites that I list in my sources.