The two are crisscrossing the state on Saturday ahead of Tuesday's key Republican primary. Arizona is also holding its primary on Tuesday.
Santorum ripped into Romney and his assertion that Santorum is not a true conservative.
Romney, meanwhile,made little mention of Santorum. Instead, he focused on the economy and his goal to give states more power.
Romney is hoping to avoid a potentially embarrassing loss in the state where he was born and where his father was once governor.
Santorum has shot up in state polls and even leads Romney in some. The former Pennsylvania senator is riding a wave of momentum after winning Feb. 7 caucuses in Minnesota, Colorado and a nonbinding primary in Missouri.
Even if Romney lost, he would still carry on with more money than any candidate and remain better organized to compete to the end.
The Associated Press contributed to this report.