When you spawn it will be easy to distinguish the two biomes as the extreme hills is on your left and the mesa biome will be on your right.
The extreme hills biome got multiple huge overhangs and extreme mountains of different sorts and sizes.
Now lets have a look at the mesa spikes biome. To get there get back to the spawn and past it. First you will see a lot of normal flat landscape mesa but once you get past all that you will finally get to the mesa spikes. The mesa spikes biome is huge and looks especially cool in this seed because there are multiple little rivers running through.