My first time with rust. What to do?

[SR5Runner97]

I'll post pics. They explain more than I can. bought this, decided to clean under the carpet and found this. I won't be cutting/welding till summer, and I have no idea what this is in the first place. Any advice/input would be more than helpful.
There is some white stuff, it powdery but also smears when tried to take off. Anyone know what this is or what can save it? I plan on sanding it down and eventually cutting the rust out and welding some metal into the place.
Also, no idea what the brownish stuff is, it's also hard to get off. Do you think it can be saved or will I have to cut it all out?
SORRY EVERYTHING IS TURNED 90 DEGREES.

 

[MStudt]

That looks like a sandy/oily mess to me. It really doesn't look that bad though, and should be pretty easy to fix. I would recommend cutting the section out and welding in a new section. In my opinion, I would always cut out the rusted and replace. There is no sense in cleaning it up and welding a new piece over it. You need to crawl under it and see how bad the underside is. If your getting rust inside, the underside might be kind of scary.

 

[sawguy]

By the looks of the carpet, it looks like someone spilled some sort of acid. Wear gloves

 

[TXLUGNUT]

^^^^^^ He's on to something...

 

[abrosk927]

Looks like a spare or secondary battery could've leaked

 

[turbo8]

Looks like some one had a battery lying on its side.

 

[BlackCat914]

A battery would've eaten through the carpet, too.

 

[sawguy]

Portable meth lab?

 

[kernel.panik]

buy some gloves!

pour baking soda and water mixture on it to neutralize the acid (if that's what it is). Shouldn't hurt if it's not.

 

[541joseph]

You can see a square mark like where a battery was sitting. Baking soda and warm/hot water

 

[TOY2G]

A battery would've eaten through the carpet, too.

It did...all it left was the plastic mat bottom of the carpet. The white stuff is a result of the sulfuric acid and hydrogen gas (just like on some terminals)

Pretty sure it is a spilled battery, and the first step is like others have said is to neutralize the acid and then start cleanup.