Landscaping Utility Easement

I would like to place 1 or 2 landscape boulders (measuring approximately 2-3 feet wide by 1.5 feet high, by 1.5 feet deep) on top of my residential utility easement.  Comcast is the only utility with a line buried in this easement.

Am I allowed to place the boulders (as my neighbors have done) or would this be considered as interfering with Comcast's access? 

If I do place the boulders, if Comcast needs to work on this area, will they move the boulder(s) and place them back again when done?  Or use will Comcast use hydroexcavation or another method to tunnel beneath the boulders?