They were using the tarp to cover their computers and other electronic equipment supplies:
Police in Houston on Tuesday night swarmed a small group of “Occupy” protesters and arrested them for possessing a tarp in a public park, according to area media.
In all, a total of 27 police officers responded to the scene in 19 squad cars, according to the protesters. Police had confronted the group around 11 p.m. about a tarp they were using to protect their equipment from the elements. It was not being used as a makeshift structure.
After about 20 minutes of negotiating, police decided to begin arresting the protesters, who refused to remove their tarp. Six individuals were peacefully arrested, and police confiscated the group’s equipment, along with the tarp. Another three were also detained for “jaywalking” and interfering with police, but later released. Three of the arrestees were released the following morning, protesters said.
They added that the equipment included food, medical supplies and electronic equipment meant to support their demonstration.