Column issues on Mobile

First of all, love the theme. Beautiful right out of the box. Thank you for this. The responsiveness seems to work great on most devices, except I’m noticing an issue with my site on mobile (specifically on the iPhone). It’s displaying two columns of blog posts when it should probably just be one. The blog title text is too big to fit. Is there a way I can tweak the CSS so it goes down to one column?

Thanks again and any help would be appreciated.

Mike