The caves of Monte Castillo form an amazingly complete series, both as regards the material culture of the Old Stone Age and from an artistic point of view.

La Pasiega is basically an enormous gallery, its known extent more than 120 meters, that runs more or less parallel to the slope of the mount, opening to the surface at six different places: six small mouths, the majority obstructed, of which two can be accessed for inspection.

While excavating the Cave of El Castillo in 1911, they received news that the workers knew of another cavity nearby, which villagers called "La Pasiega."

"In the next decade, Alcalde del Río was to assist fully in the international project that the Institut de paléontologie humaine in París sponsored, in which Abbé Breuil and H. Obermaier were prominent.

Therefore, a geological survey was set in motion which resulted the following year in the discovery of another cave with rock paintings, "Las Chimeneas" ("The Chimneys"), and also other covachas of lesser importance such as "La Flecha", "Castañera", "Lago" etc.

The cave, because it had remains of the primary Cantabrian Solutrean and Magdalenian epochs, provided the basis for a chronological series for the 'wall' paintings.

The most recent layer was also relatively rich, with various burins (borers), striker pins, and perforated objects of bone and that could belong to the Lower Magdalenian.

Certainly, compared with the stratigraphical significance of El Castillo, La Pasiega is an archeological sequence of less organization, so far as the materials yet found are concerned.

Joaquín González Echegaray[10] and later his fellow-workers[11] have made various counts of the species of animal represented, one of which reckoned more than 700 painted forms in this cave, among others: 97 deer (69 females and 28 males), 80 horses, 32 ibex, 31 cattle (17 bison and 14 aurochs), two reindeer, a carnivorous animal, a chamois, a megaloceros, a bird and a fish; also there may be a mammoth and about 40 quadrupeds not clearly identified; also the idiomorphs, such as roof-shaped and other surprisingly varied symbols (more than 130), and very often including various anthropomorphs and hundreds of marks and partly erased traces.

Entering into the cave, one passes a blocked entrance on the right, and between 60 and 70 meters depth appears the connection to Gallery B, slightly before the most interesting collection of pictures.

The paintings can be put together in various groups, paying attention, above all, to dating criteria, but also technical and thematic sequence which unfolds like clockwork.

[note 3] The First Large Group is on the left hand wall of the gallery, including figures arranged as a double frieze with numerous deer, mostly female, and also plenty of horses and a bison which is at the centre of the composition.

They are clearly dominated by deer in association with some idiomorphs and a few cattle (possibly aurochs), which seem to stand in relation to the horses in the group which next appears round a corner.

The Second Large Group begins around a bend to the left, in the end area of the gallery, where it becomes narrow: it brings together figures on one side and the other.

"[12] The cattle are concentrated on the right side, together with three of the horses, forming the nucleus of the binary dialectic arrangement of this second group, and moreover, there is also included with them the anthropomorph, all surrounded by the typical peripheral animals (deer) and idiomorphs.

On the left wall, together with more deer, the other five horses which apparently stand in binary relation to the cattle painted before the bend, which have been mentioned in the earlier description.

The predominant technique, for its warmth and for its frequency of use, is the tinta plana - the plane or block color – either combined with black lines forming an outline in a sort of two-color method (as occurs on one of the horses), or emphasized with engraved lines which define details (this can be seen on various hinds), or enclosed, with scraffito in the rock to add chiaroscuro textures, as happens with a hind painted in red.

Among the various symbols an idiomorph in the shape of a hand is prominent, reminiscent of those at Santián,[13] and a red sign which could well be meant for a grotesque bison head.

But it is outstanding for the originality of some of its other figures, including a fish, a large ibex and idiomorphs like rods, key-shapes and an unprecedented little group of symbols popularly known as "The Inscription".

Immediately before reaching the centre of the large room there appear signs on both sides, but this time they are of the beta type (feminine), red in color.

The techniques employed by the painters recall, partly, those of Gallery A (which is why they have come to be considered as related rooms): red painting, between modeled and outline, red block coloring (tinta plana), with some internal modeling achieved by scraffito to the underlying rock and by the addition of lines of the same color but in more intense shades.

Leroi-Gourhan differentiates two clear parts to this sanctuary, located in separate places within the same room, and with different themes, technique and chronology.

Clearly the dominant technique is red outline drawing, but in one of the panels is also found, for some deer, striated engraving of very fine execution: also, there are various figures in black.

In addition, there is two-color work on one of the cattle, in which red block painting and black lines are combined, this time a repainting of different date.

The species represented show predominantly horses, followed by cattle, and fewer but certainly present are deer and ibex (for which the symbols are complementary to the foregoing group).

However, there are plenty of isolated figures, above all round the entrance to the room from Zone D. The dominant techniques are engraving of multiple lines, as if striated, and black painting: the yellows, reds and ochres are fewer.

This is an intermediate part of the cave, which is probably an extension of the sanctuary of Gallery C, like a 'grey area', with much fewer and more sporadic images among which there is little coherency, apart from a pair of small groups which continue to repeat the theme of the cattle and horse dualism.

The idiomorphs – and possible anthropomorphs – of La Pasiega are listed and classified as: In the second type, the dots can appear much more loosely grouped.

But more important are the tinta plana red paintings treated with modelled chiaroscuro, sometimes associated with graved or black lines which complete them: These are the ones which express dynamism most of all (twisting of the neck, movement of the legs, etc.).

Jordá maintains that, during the Middle Cycle, the anthropomorphs disappear, even though La Pasiega contains a few: according to the oldest authors four, and according to the most recent only one.