Thanks to Vorkir we can now load our trucks with small or large rocks. Which can potentially be used to dam a river..
Drive carefully as the rocks can damage a truck when they bump around. And you may need to edit your dumper xml to give it more strength to lift the bucket.
To load rocks you need to drive to a lumber yeard. Once there you can choose small or large rocks. Once you load up press V for advanced and there you can load the rocks. Make sure the truck is parked level.
And here is a example of what can be done with these rock loads.. build a dam in the river!