my brake rotors have ridges

i can feel the ridges, and today when i got the tires rotated and balenced i went in and looked, and you can see the ridges...easily...more so on the passenger side than driver'*....i think some rocks probaly got up into the brakes....and there is a vibration when i stop slowly and under 20-25mph...if i stop like a second before the last second to stop its smooth....

That'* not completely uncommon. Your rotors are just worn. If you're getting a vibration when stopping then your rotors are slightly warped. Consider new pads and rotors to correct it.