Tex. Natural Resources Code § 53.011

Any tract of land that belongs to the state, including islands, salt and freshwater lakes, bays, inlets, marshes, and reefs owned by the state within tidewater limits, the part of the Gulf of Mexico within the state's jurisdiction, unsold surveyed public school land, rivers and channels that belong to the state, and land sold with a reservation of minerals to the state are subject to prospect by any person for those minerals which are not subject to lease or permit under any other statute. A person may not prospect from a location within 2,500 feet of a military base, but prospectors may, from a location more than 2,500 feet from a base, look for minerals within the 2,500-foot strip.