I've made this hill from 6 parts and mated them together.

I've to place two lines running from the bottom of the hill to the top, as seen in the picture however I don't want to cut them all the way through the hill surface, I only want them to cut a groove into the top, almost like a path. I'm new to SolidWorks so not sure if it is better to go back to the individual parts to try this or can it be done from an assembly? The path follows a set line from a sketch.

Thanks for your support,

Fionn