The primary access road to the valley runs on the side of the north scarp throughout its entire length.

The true sources of the water in the upper Pleistos are the numerous springs that exude from the base of the north scarp, and waterfalls that pour over it.

This water in all the cracks breaks out rocks by freezing and thawing, while in the soil of the scree it contributes to the fluidity, making landslides more likely.

Rockfalls and mudslides are common along the valley, making protection by steel mesh fences a necessity in places, and closing some features of Delphi to the public.

The river begins from sources on the side of Mount Parnassos below the town of Arachova, Boeotia, at approximately 38°28′34.8″N 22°35′26.8″E / 38.476333°N 22.590778°E / 38.476333; 22.590778.

The river enters the Gulf of Cornth undramatically through a culvert of the coastal road on the east side of Cirra.

A stream a few inches deep leaves the culvert to cross a small delta, geologically of antique origin.

The wetland originates further north from a ravine in Mount Cirphis, but it does not receive any waters above ground from the flow of Pleistos.

[3] They cover the entire non-urban areas of the valley system and are called locally "the sea of olives."

During the reconfiguration of the hydrology, the Pleistos was disconnected from its wetlands and forced to irrigate olive trees.

The upper Pleistos and its valley are protected: no industrial artefacts are to be seen from Delphi (for example high voltage power lines and the like are routed so as to be invisible from the area of the sanctuary).

Over geologic time the sum of very small deformations under steady pressure gives the impression of a flow.

The Hellenic orogeny is part of a 15,000 km (9,300 mi) zone of convergence called the Alpide belt.

The African Plate moving northward closes Tethys Ocean, the much vaster ancestress of the Mediterranean Sea, and raises the Pyrenees, the Alps, and the mountains of the Balkans.

The -ides suffix was the innovation of Eduard Suess, author of Das Antlitz der Erde ("The Face of the Earth"), and contemporary of Wegener.

The zone stretched from the Pacific to the Atlantic, dividing Pangaea into two forelands, Eurasia and Gondwana Land.

Tethys received sediments from the adjoining lands until at last they were compressed upward to become roughly parallel mountain chains striking in an E-W direction (with local variants).

The line of subduction of Africa under Eurasia runs in a general E-W direction through the Mediterranean.

The southern margin of Eurasia rises over the subduction to become the mountains of the Alpide Zone as though they were folded up by compression, and to some extent they are.

One should therefore expect to find compression also beyond, or inward of the raised margin of the overriding plate, but this is not entirely the case.

The outer chain of the ridge resulting from the orogeny has broken loose and bent southward into the Hellenic arc.

Another, younger rift (1 Ma), the Pleistos Valley, has opened to north of and parallel to the Corinthian Gulf.

Fortuitously the gap at the top of the scree resemble the vulva, inspiring a specific mythology of the "mother Earth" type.

There may have been an augmented release of gases due to the intersection of faults, which may have inspired the oracular priestess, but the theory has not been proved.

The rift is relatively recent, the separation is slight, and a scarp is still visible all the way from Amphissa to the head of the valley.

In modern times the access problem was solved by leveling the top of the scree and building a road there.

The highway is good, two-lane, hard-top road, which gains or loses altitude in a few places by some hairpin legs.

Many parking areas for viewing have been excavated into the scarp or placed on filled extensions to the width.

They give the illusion of the scree merging directly to the bare scarp, which only happens at the top of the upper site.

Solon of Athens is said to have used hellebore roots to poison the water in an aqueduct leading from the River Pleistos around 590 BC during the siege of Kirrha.