Why is 30MHz Clock signal distorted on oscilloscope?
There are two issues here: Bandwidth and Measurement technique.

Bandwidth: 
Your measured signal is bandwidth limited. A 30MHz square wave has lots of harmonic content and your scope has a relatively low bandwidth (200MHz) so the higher frequencies are attenuated and you only see the sum of the first few odd-order harmonics (30MHz, 90MHz, 150MHz, ...).

Here is a square wave approximation made up of the 1st, 3rd, and 5th harmonics (taken from this question which looks quite a bit like the trace you posted: 

Tektronix has a Technical Brief on this subject that might be of interest:

Understanding Oscilloscope Bandwidth, Rise Time and Signal Fidelity



Measurement Technique:

You are using a rather long ground clip which contributes to overshoot. This answer to another E.SE question illustrates the improvements in measured overshoot by using a spring clip on the scope probe tip instead of the longer ground tip.

Before: 


After: 


Here is the measurement setup: