Clock Signal on Clone number 2

This is a shot of the clock signal on the 6502 / PIN-37
The peak is at 4 volts, and the frequency is 1.020 MHz. Horiz sweep is 500.0 ns.
I'm not sure why there is a negative spike in each cycle?
You can see the same spike in one of the photos below, on the analog scope taken from Clone number 1.