When I pedal hard or even stand up and pedal on flat surfaces i hear a sound that sounds like rocks rolling around in a tumbler. In certain gears the sound occurs even on level ground at normal pace. I think it might be bearings in the bottom bracket but I'm not sure. And is there any way to determine the size of the bottom bracket without actually taking it apart? I contacted the manufacturer but got no information.
Try watching Alex's video to determine.. http://bicycletutor.com/check-bearing-wear/
. A picture of the bike would really help if you can manage one.
Good maintenance to your Bike, can make it like the wheels are, true and smooth!
Also, try flipping the bike upside-down, drop the chain off the inner chainring, so that the chainset is completely free. You should now be able to feel for any play in the bottom bracket, or rough or overtight bearings.
Remove the wheels as well and check the hub bearings while you're at it.
Once everything's OK it should be good for a ride around the dunes. ;-)
Having seen the pictures; never mind all that, look at the state of the chain! It's totally dry and completely coroded.
For starters, fit a new chain, and once you have keep it well lubricated, your existing one is almost certainly beyond salvation.
When you remove the existing chain, clean up the rest of the drivetrain and make sure to keep everything well oiled once you fit the new chain. You don't really want to overdo the lubrication, but to some extent, too much oil is better than not enough, or none at all.