Switching majors is easy to do, just talk to your major advisor. My roommate switched his major when he was a junior because he realized he didn’t like chemistry (epiphany during ochem). So it’s not like you need to know exactly what your major is right away.
But, the Geology department is pretty cool. I’m not sure how big the department is, but it has a pretty active Geology Club that has a Facebook page if you want to join. Everyone is also very friendly and seems to know each other well after being in the same classes for a few years, especially from all the field work ^^. The class sizes for GEL are very large for lower-divs (people like GEL classes for GEs) and are moderate for upper-divs – many upper-div classes are also taken by other science and engineering majors, so you meet people from outside your major. The main building is the Earth & Physical Sciences Building, and on the first floor is a little room for students with a fridge and a REALLY comfy chair, so make sure you swiftly locate that.
The prep for the major is fairly standard, so you could likely switch to a different science or engineering major pretty easily with that foundation (math, chem [try to get Prof. Enderle!], physics, etc.) if you decide geology isn’t for you. From what I’ve taken, the courses in the major are interesting and each one is valuable; I think the major is formatted well and has good professors. My favorite was GEL108 with Spero, and 107 and 109 were fun (and pretty easy compared to the other ones) too :3.