do I need a table function to do this?

I have been given an interesting problem to solve in a postgres db. I was given two tables

t1:

site treatment variable id (pk)
-------------------------------------------------------------
A X BLUE 1A
B Y RED 2B
A Y GREEN 3A

t2:

rowid (pk) timestamp BLUE RED GREEN
-----------------------------------------------------------------------------------------
1 1332493200 3.4 2.1 5.8
2 1332496800 3.2 2.0 5.8
3 1332500400 3.3 2.2 6.0

I need to combine the site and treatment information from t1 with the variable records in t2. I think I will have to combine these one variable at a time. Something like this (I'm not using the word join, because I don't think this is a join in the regular sense. It's more like some kind of crazy pivot table thing!):

t3:

rowid (pk) timestamp BLUE site treatment
-------------------------------------------------------------------------------------
1 1332493200 3.4 A X
2 1332496800 3.2 A X
3 1332500400 3.3 A X

and then:

t4

rowid (pk) timestamp RED site treatment
-------------------------------------------------------------------------------------
1 1332493200 2.1 B Y
2 1332496800 2.0 B Y
3 1332500400 2.2 B Y

Is this even possible?