FYI: In case you use this figure for anything that matters, you've got a couple of labels that have the attenuation in Hz instead of dB.If you have an FFT function, you can see the harmonic content of that sine wave.
Below is a panoramic view of the 60 Hz at my shop when I was in western Oklahoma, about 125 miles N of Amarillo TX. The generating plant was in Amarillo.