Rick you cannot take free relief from thick or uncut rough. If you find your ball in thick or uncut rough you can play it as it lies or declare it unplayable (Rule 19.1) and proceed accordingly. After three minutes if you cannot find your ball after hitting it into thick or uncut rough it is considered lost (Rule 18.2).
The only way you would receive free relief would be if there is temporary water. They have changed the rules for temporary water, so be cautious, an accumulation of water must remain present either before or after the stance is taken. If the area is wet, muddy or soft, that no longer meets the standard for temporary water.
You always have the option to play a second ball (Rule 3.3) and advise the committee when you turn in your card and they can tell you how you proceed.
I think I got it all, Bob Newman may add something I forgot to include.
The USGA will mail you a free rule book if you request one from their web site, they also have an app and a complete listing on their web site.