The hills are made of basaltic andesite and trachyandesite lavas erupted during the Early Devonian, when this part of what would become Scotland was a series of volcanoes. The Ochil Volcanic Formation, a sub-unit of the Arbuthnott-Garvock Group, piled up thick layers of lava and ash. Around Blackford and Auchterarder, on the northern slopes, you can still see volcanic conglomerate where chunks of older rock got cemented into the flows. The whole massif is heavily faulted, intruded by dykes of microdiorite from the Silurian-Devonian Calc-alkaline Dyke Suite that runs across northern Britain. Glaciers later did the polishing, scouring out the corries on the south face and gouging deep glens that hold burns rushing down to the Forth. Dollar Glen, Silver Glen, Alva Glen: all narrow, all dark, all impassable in places without wooden walkways.

The Ochils were once Pictish country. Castle Craig, a hill fort above Mill Glen, was described by local historian William Gibson in 1883 as a round Pictish fortress whose traces could still be distinctly seen. Industrial quarrying has since erased it. Local lore claimed that some of its stones were carried west to build Stirling Castle, an oral tradition that may or may not be accurate but speaks to the way the Picts felt close even in the 19th century. Higher up at the eastern edge of the range, the great crags of Dumyat are credited with holding the last Pictish stronghold in the area, an old hill fort whose name survives even though its walls do not. Pictish researcher Ronald Henderson has argued that Katie Thirsty's Well, an unexplained sacred spring in the hills, takes its name from a corruption of St Katherine of Alexandria and the Pictish king Drust. Whether or not that etymology holds up, the Ochils are full of names whose origins have been forgotten by everyone except the wind.

From the top, the Ochils feel less like a range than a great undulating tableland. Ben Cleuch at 721 metres is the highest point, but the plateau rolls on with no commanding summit, just a long series of rounded tops separated by peaty hollows. Ben Buck reaches 679 metres, Andrew Gannel Hill 670, King's Seat Hill 648. Walkers climbing from the towns at the foot of the scarp, from Tillicoultry or Alva or Dollar, get the dramatic ascent. Walkers approaching from the gentler north, from Auchterarder or Blackford, hardly know they are gaining height until they look back and realise the country below has dropped away. The Ochils Mountain Rescue Team, founded in 1971 and based at the foot of the hills, fields 35 volunteers who pull people off this deceptively friendly plateau when weather closes in. A Cessna 152 crashed between Andrew Gannel Hill and The Law in 2006. The pilot walked away.

Twenty-first century use of the Ochils has added a new layer to the older economy of sheep and hill walking. An 18-turbine wind farm was approved in June 2006 at Green Knowes, south of Auchterarder, just north of the Ben Thrush summit. A second wind farm at Burnfoot Hill, north of Tillicoultry and south of the Upper Glendevon Reservoir, was completed after 2007. Burnfoot Hill carries fifteen 2 megawatt turbines and six 2.05 megawatt turbines with tip heights of 100 metres. EDF Renewables, which owns the site, supports the Ochils Mountain Rescue Team through the Burnfoot Hill Community Fund with a guaranteed annual donation of 5,000 pounds running until 2039. The turbines have changed the skyline that walkers see from the south, but they have also made the old plateau pay for itself in a way that the Pictish hill fort builders would have understood: a high place, a strong wind, a way of turning landscape into something useful.