Master hill mostly resembles a brighter version of beginner hill and alpaca hill. You unlock it when you obtain an alpaca of level 45.
When you first unlock it, the alpaca inside will still out level you as the first part of master hill contains alpaca from level 59-66; so you will still have to power up in white or black hill to start catching in master hill.
Unlike white and black hill, the alpaca in master hill's colors aren't as restricted and can be the more vibrant (albeit less valuable) greens and blues. The trade off in value can be worth it though, as the level of alpaca in master hill can be up to and possible greater than level 90.
It is currently confirmed that both black and white alpaca spawn in master hill, but it would be advisable to look for them in white or black hill as they have a significantly higher spawn rate there. Master hill is a lot like alpaca hill except the alpaca level is significantly high.
Less valuable alpaca fur colors are also found here (vibrant colors) but light and dark colors are also proven to lurk around here. Before capturing alpaca from here you will need to crunch up an alpaca to really high so you can fight the higher level alpaca.