Its upper reaches are occupied by the town of Tredegar within the county borough of Blaenau Gwent.
The valley initially runs south-southeast between the ridges of Cefn Manmoel to the east and Mynydd Bedwellte to the west before turning to a more southerly direction.
The valley enters the county borough of Caerphilly, which contains the towns of Blackwood (Welsh: Y Coed Duon) and Pontllanfraith.
Coal mines used to be located throughout the valley, including: Wyllie; Nine Mile Point and Oakdale.
Prior to the Beeching Axe, the valley was served by the Sirhowy Railway,[3] with stations at many points including Nantybwch, Argoed, Blackwood, Pontllanfraith and Ynysddu.