The fine piece of ground called 'Cat-stones,' is enclosed on three sides by a considerable bank of earth, and bears evident marks of the plough. The country people believe it to have been an intrenchment or camp.
p81 in William Keighley and Robert Holmes's 'Keighley, past and present' (1858) - viewable on Google Books. They also say, clearly about the same area:
On Harden Moor, about two miles south of Keighley, we meet with an interesting plot of ground where was to be seen in the early days of many aged persons yet living, a cairn or 'skirt of stones,'* which appears to have given name to the place, now designated Cat or Scat-stones. This was no doubt the grave of some noted but long-forgotten warrior.
*The Cairn was called Skirtstones by the country people in allusion to the custom of carrying a stone in the skirt to add to the Cairn.
There are a group of cairns still on Harden Moor, though these are to the NE of Catstone Hill, curiously, around SE 075 386. So maybe the one they refer to really has gone.
The information from the SMR on Magic says the site is a 'late prehistoric enclosed settlement' and that quarrying has destroyed much of the west side. An excavation in 1962 didn't turn up many artifacts: perhaps it was mostly used for stock, but there is/was a bank and ditch. A Roman road runs north-south about 100m west of the site.