Texture issues.

My board game has a number of different terrain types, including the basic lava, water, rough terrain, and open ground. Water and lava are super easy to do, as is open ground (grass, dirt, snow, etc.) Rough terrain and impassible hexes are the tricky bits, though. I’m not sure how to show with just textures that a hex is impassible or difficult to traverse. I’d thought about using a rubble texture for rough terrain, and a rock texture for impassible, but I worry the rock texture would be too easily mistakable for open ground. One solution I’d thought of is using parallel lines over the rough terrain texture, and crosshatched lines over the impassible terrain. This would let me have multiple textures of each, but I worry it would be jarring/incongruous. Any thoughts?