After spawn in front of you is a river. The mesa biome is on your left but first you need to cross the river, but before try to find the main section of this seed, let’s explore this mesa biome first, it look so cool with mesa hill and the river flowing around.
You can see as the images above is a open cave, cross it or you can fly past over it and you come to other large open area with lot of mesa stone arounding. Somewhere in that area is some spot some rails and that is first sign of the surface mineshaft.
And this images is entrance of mineshaft, no need to digging because it is open cave and it leads down into some tunnel. Moreover if you try to looking careful around you can find some other opened mineshaft. Some time you met some glited but it doesn’t a big problem.