EDIT: Woops! I figured it out. A combiner node using the Max method.
I've been trying to figure out how to get a height blend that is a result of 2 height inputs, where the higher value of each pixel is fed to the output.
I'm having trouble figuring out how to do this with the nodes that world machine provides, though I believe I could do this with the height chooser if I could generate a proper guide input. Any advice in this regard would be very appreciated. Here's an illustration of what I'm going for.