>>1
Calc, trig, and geometry as you think of them (which is in the high school sense) are elementary and have little to do with what actual math is. The fields you will start to get into as an undergraduate math major are linear algebra, differential equations, real analysis, and abstract algebra. If you want to see what those are like, here are the books my college uses:
- analysis: Principle of Real Analysis by Rudin
- abstract algebra: Introduction to Abstract Algebra by Hungerford
- differential equations: Elementary Differential Equations by Boyce and DiPrime
- linear algebra: Applied Linear Algebra, by Shakiban
In real analysis, you will start with the definition of a set and work your way up to proving all the theorems you learned as "just true" in calculus. If you're interested in geometry, look into differential geometry. The book my school uses sucks, so you're on your own for that one.