Join Date: Sep 2018
Location: Mission British Columbia Canada
At 3' x 4' I'd replace it.
You're going to spend a lot time sanding and making a big mess only to find out the salt and dirt is deeply embedded in the wood, To sand it down to where there is no dirt with a orbit sander will take a long time and it will be hard to keep it all level.
If you buy new hardwood it will be flat, clean and level. It probably won't take much longer to install because it will only need a light sanding, You could be done in one day and have it look brand new.
Since it's a small size you could probably get someones leftovers for cheap, do you have a Re-use-it store in your town? Craigslist is another good place to find contractors leftovers, You can get small quantities cheap because the original customer paid the contractor for all of it and he's selling the leftovers after the contract is finished for beer money.
Good Luck, let us see how it went.