Widget area height relative to sidebar height

Thanks to juggledad for helping me split a sidebar into two widget areas to mimic two sidebars. One lingering question:

I used CSS to place a border on the left of the farthest right-hand widget area to mimic the sidebar border, but since the widget area doesn't go to the bottom of the sidebar, the border doesn't either. What's the best way to force it to continue to the bottom so the border is complete? (The site is http://www.localoranges.com for reference).

Thanks again!