Black Rock Depths is an instance located in Blackrock Mountain, which sits between Burning Steppes and Searing Gorge. 

Mobs: 

• Humanoids
• Beasts
• Elementals.

Drops: 

• Runecloth
• Recipes
• Greens
• Grey Vendor Trash
• White Vendor Trash
• BoE Blues
• Gems

Pro's: 

• There is a vendor inside the instance at the entrance. 
• There are teleporters to various parts of the instance.
• Some skinnable mobs.
• If you haven't completed the Molten Core attunement quest, you can enter Molten Core from the instance.
• If you have mining, you can mine the Dark Iron veins throughout the instance.

Cons:

• Its a fairly long instance so set aside plenty of time.
• Bags can get full without vendoring the trash items
• Mobs will often leash back to their original position so make conservative pulls.

Before I started, I emptied my bags and relogged to accurately track my gold looted/vended through out the dungeon.

These are the drops I got.

Gold:

• Looted: 11g 17s 69 copper
• Vendor Items: 49g 61s 70c
• Total gold: 60g 79s 39c

Drops:

• 21 BoP Blue items - Vend Value 51g 80s 26c
• 296 Runecloth
• 4 Mithril Lockboxes
• 1 Reinforced Steel Lockbox
• 1 BoE Blue - Spire of the Stoneshaper
• 4 Transmog Greens
• 14 Vendor/De Greens
• 19 Black Diamonds
• 1 Recipe: Limited Invulnerability Potion
• 1 Recipe: Elixir of Giants
• 1 Plans: Dark Iron Plate
• 3 Star Ruby
• 1 Essence of Fire

Looting the relic coffers gave me several small bags of gold (The amount is added in to the Looted gold total) and 3 sacks of gems.

The sacks of gems yielded:

• 4 Tigerseye
• 4 Moss Agate
• 2 Lesser Moonstone
• 2 Jade
• 2 Malachite
• 1 Shadowgem
• 1 Citrine
• 1 Small Lustrous Pearl
• 1 Black Pearl

Lockbox Items:

• 1 Transmog Green
• 1 Blue BoE dagger
• 4 Vendor/DE greens

BoP Blue Disenchanting Yields:

• 6 Small Brilliant Shards
• 15 Large Brilliant Shards

The Green items disenchanted into:

• 1 Large Radiant Shard
• 2 Lesser Eternal Essence
• 2 Greater Eternal Essence
• 29 Dream Dust
• 2 Greater Nether Essence

There are also 2 vendor recipes available inside the instance. Yuka Screwspigot is an Engineering Supplies Vendor (also the vendor you sell the junk to during the farm run) and she sells Schematic: Deadly Scope for 30s. Plugger Spazzring who is located inside the Grim Guzzler, sells Pattern: Black Dragonscale Breastplate for  2g 52s 13c so if you need this, or want to buy one for sale on the AH, make sure you purchase this before you kill him.

In conclusion, whilst the actual gold looted does not seem that good, the instance more than makes up for it with the amount of greens, BoP blues and various AH'able drops that it hands out.