Half the Deccan is old lava and the other half is old granite

A plateau is not the same thing as a plain

The Deccan is raised ground rather than flat ground, and the distinction matters as soon as you try to move across it. It sits well above sea level, it is tilted gently towards the east, and almost all of its major rivers — the Godavari, the Krishna, the Kaveri — run east across it to the Bay of Bengal despite rising within sight of the western sea.

Relief on the plateau is low, but it isn’t absent. The country rolls, ridges run for tens of kilometres, isolated hills stand up out of otherwise open farmland, and the interior is broken by shallow valleys that a map at national scale simply cannot show.

What gives the region its edges isn’t its middle but its rim. The Western Ghats form a steep wall along one side, the Eastern Ghats a broken and lower one along the other, and between them lies an interior that has always been reached by climbing up to it.

The northwestern half is stacked lava flows

A very large area covering much of Maharashtra and running into neighbouring states is made of basalt laid down as successive flows of lava, one on top of another, over an enormous span of time. Each flow cooled into a layer, and the layers are close to horizontal, which is why hills in this country so often have flat tops and sides that step downwards in ledges.

Travellers notice the shape before they know the cause. A skyline of level-topped hills with terraced flanks, all of them ending at roughly the same height, is the signature of the trap country, and once you have seen it you will keep seeing it for several hundred kilometres.

That rock is also why the region has the cave monasteries it does. A thick, uniform, joint-free layer of basalt is the ideal material for excavating into rather than building on, and the great rock-cut sites of the Deccan sit exactly where the flows are thickest.

The southern plateau is granite, and granite makes boulders

Move south and east — into interior Karnataka, into the Rayalaseema country, into parts of Telangana — and the rock underfoot changes to ancient granite and gneiss, some of the oldest exposed material anywhere on earth. It does not weather in layers. It weathers into rounded masses, and the landscape it leaves behind is one of tors, domes and stacked boulders that look precariously balanced because they are.

This is the ground on which Hampi sits, and the reason Hampi looks the way it does is geological before it is architectural. The boulder fields were defensive, they were quarries, and they were incorporated straight into walls and gateways wherever it was easier to build against a rock than around it.

Granite is also a harder, more brittle stone to carve than basalt or sandstone, which is part of why the temple sculpture of the southern plateau has the crisp, angular, deeply undercut quality it has. The material was pushing back.

Black soil and red soil behave very differently in rain

Basalt weathers into a dark clay soil, often called black cotton soil, and it has a property that matters enormously to anyone leaving a metalled road. It swells and turns greasy when wet, then shrinks and cracks open when dry, and a vehicle track across it in the monsoon can become genuinely impassable while the highway two kilometres away is fine.

The granitic south weathers instead into red and sandy soils that drain far better and hold far less. Unsurfaced roads there are usually usable in the rain and dusty for the rest of the year, which is a different set of problems and, for a traveller, a milder one.

None of this is academic. It decides which village roads are worth attempting after rain, why some field tracks are abandoned for months, and why local drivers refuse routes that look perfectly reasonable on a screen. When somebody who lives there says a road is closed, they usually mean the surface has stopped behaving like a surface.

Crossing the interior is a distance problem, not a terrain problem

For all its variety, the plateau is easy country to drive compared with the hills on either side of it. Gradients are gentle, the trunk roads are mostly good, and average speeds hold up in a way they never do in the Ghats. What you pay instead is distance, because the things worth stopping for are strung a long way apart.

The interior is also dry. Much of the plateau sits in the rain shadow of the Ghats and receives a fraction of what falls on the crest a short distance west, so the season here is short, the winter months are the comfortable ones, and the pre-monsoon weeks are hard work outdoors.

The most useful adjustment is to plan around a few nights in ordinary towns rather than trying to reach a famous one every evening. The plateau rewards that; its old routes are marked by market towns, temple sites and fort hills at fairly regular intervals, and driving past all of them to arrive after dark is a poor trade.