Need help with sectional chart.

I’m just learning to read charts and can’t figure out what this is. What does this blue circle with these tick marks mean on this chart?

And if I am flying in the class C 84/72 area but below 7200’ am I in class G airspace?

I’m just learning to read charts and can’t figure out what this is. What does this blue circle with these tick marks mean on this chart?

And if I am flying in the class C 84/72 area but below 7200’ am I in class G airspace?