Stone flags have been torn up at Castle Hill, prompting calls for the site to be locked off at night.
Security has long been a problem at the beauty spot – a flat-topped Iron Age hill fort dating back 4,000 years.
Since the demolition of the 19th century Castle Hill Hotel in 2003 there has been no regular presence on the landmark.
The latest incident, which has been reported to police, occurred on Wednesday night and was discovered by a park ranger.
The flagstones were lifted from the footpath directly in front of the entrance to the 122-year-old Victoria Tower.
However the paving slabs are said to be watermarked, which will indicate their origin if they are sold on.
It is the latest in a series of targeted stone thefts at Castle Hill.
Kirklees Council is now being urged to lock and secure the site after dark.
The authority does not allow camping, barbecues or fires at Castle Hill, and discourages kite-flying and the use of kite buggies.
Clr Bernard McGuin (Con, Almondbury), whose ward contains Castle Hill, said: “The road up to Castle Hill should be locked at night.
“If anyone wants to exercise a dog up there they can park their car and walk up.
“Or they can take the steps. I know that would inconvenience disabled people but it would stop flagstones being stolen.
“Put it this way: I’d like to see a thief carry them down by hand.
“No-one is based at Castle Hill anymore. There’s no reason for anyone to be up there after dark.”
He asked: “Is it time to make it secure and to lock it at night?”
Ian Gledhill, proprietor of Huddersfield-based PG & Son Stone Sales, said good quality flagstones were valued at between £60 and £80 per square yard.
“A lot of it is stolen to be sold online and taken down south.
“Honest reclamation yards won’t accept it without asking for identification. A lot of these thieves know each other.
“Castle Hill is a target because it’s secluded and dark.”
In 2006 Kirklees Council announced plans to introduce a curfew for cars following reports of “dogging” – people participating in or watching public sex outdoors – at Castle Hill.
In 2009 West Yorkshire Police said it would introduce extra patrols at Castle Hill, which at that time had been a notorious dogging hotspot for as long as 30 years.
A Kirklees Council spokesperson said: “We can confirm that a number of stone flags have been stolen from Castle Hill.
“This is absolutely disgraceful and we will be working closely with police to catch those responsible.
“Thieves should know that we mark these flags with invisible ink so we’ll be able to identify them very easily.
“Castle Hill is a beautiful and iconic place which Kirklees is incredibly proud of and it’s really disappointing that selfish people can show such disrespect in this way.
“It’s a shame that we feel the need to have to do this, but we will look into the possibility of increasing security at the site.”