Two ways I can think of immediately that would do this for you.
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Duplicate your landscape and break off the landscape components from your cliff into one landscape and the grass for the other and leave tessellation on for just the cliff - but then you may have to work hard to make the transition areas between the two landscapes smooth.
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Turn off tessellation on the cliffs altogether and instead create static mesh cliff sides, with or without Tessellation and embed them against the sides of the cliff.
I’d go with option 2 honestly, that’s going to get bigger and better shadow shapes and less tiling issues, but option 1 would be great if you can make the transition areas look clean.