Multiple terrains. How do I connect them?

Unity Engine
1

I made a nice little valley in Unity and then I created a new terrain to add on to the valley. I would really like to connect the two terrains together instead of having to tediously raise and lower the height map just to fit perfectly. Just in case you need dimensions:

Valley Terrain 1 -
Width: 300
Height: 300
Length: 300

Valley Terrain 2 -
Width: 400
Height: 200
Length: 400

2

There’s Stitchscape, however the terrains have to be the same size/resolution for that to work.

–Eric