Sadie and Adventure Girl, thanks for your inputs and help.

Do you get the drivetrain wet and then take it through sand? What happened?
not sure what happened... i guess i did but i don't remember riding through much sand. i tried cleaning with solvent and a rag but as adventure girl said, and i learned today, the sand in the cassette got back on the chain.

I take the chain off and clean it. Then I take the cassette apart and clean the gears in a solvent tank. Then put it all back together. It's kind of a pain, but worth it in the long run.
I was hoping not to have to do this. I guess that Park tool that Sadie suggested doesn't clean the cassette, just the chain? I have no clue how to take the chain and cassette apart. I just got this bike last week! This may be the time to invest in a bicycle repair/maintenace book. I'm an engineer... I think I can figure this out... I hope! Will I have to do this everytime I ride and find sand in the drivetrain?

Should I try anything else before diving into taking things apart? Should I take it to my LBS?

-feeling so clueless and sad that i may not be able to ride tomorrow.