That involves CALEA intercepts and other intercepts by law enforcement — which is different than unidentified cell towers. They don’t need special cell towers to track communications - they can use the carrier equipment and just call in an intercept whether it is cellular or wifi. My guess is the cell towers are military.
They can listen in to any phone call in the county and track it, right from their van. If they were going through the phone companies, they would need a warrant, they do not have warrants for what they are doing.