One of our pages shows up with only the title, and all the other content is missing. But when I go to edit the page, the content is all still there. Even the visual editor shows what the page normally looks like. But the page itself is blank.--> http://sierraclubcalifornia.org/news/

I've tried making a new page with the same content, which also ends up blank. I've tried turning off all my widgets, and un-doing the changes I made to the index.php; but that did not make a difference either. I have no idea why this would have happened--I can't think of any changes made to the page between when it was working to when it stopped working (although, I am not the only one that works on the site, so someone else certainly could have done something...).

I'm posting the html here in the desperate hopes that someone may know what's wrong.

what happens if you remove the current content and just put in 'hello world'? Does it show up?

I'd try changing permalinks back to default, then back to current setting (numeric?), that sometimes fixes things.
Or look at the nav and pages (and its permalink), make sure the same News page is the one that your nav is looking at.

FYI, it has something to do with the data in that page. I put it in a page and it doesn't display, but when I remove all but the first line, the first line shows.

I suggest adding chunks in till it fails and you'll know what is causing the issue.