Is My Trap's Challenge Rating Correct?

[KissMeDarkly]

UGH. I actually had to walk away from the computer before I could return to this post, because I had to re-type this entire post. Here goes.

So... I downloaded PF BETA and almost immediately I looked up the Trap Creation Rules (pg. 308). I decided to work out a couple of traps. I was also uncertain about how to make my "Death by Four Elements Room" work exactly the way I wanted it to. I finally decided that using the Timed trigger to set off the traps after the first one is activated. I'm not 100% sure if I've got the CRs right.

This trap I call the "Pillar Slam Pit".

The Details: The room is 70 ft. long and 60 ft. wide. After entering the room it is only 5 feet before reaching the pit. The pit is 60 ft. in all its dimensions (length, width, deep.) Each pillar is 1 ft. wide and the center of each pillar is exactly 4 ft. from the center of the neighboring pillars. The ceiling is 15 ft. above the floor and the pillars.

Description: The room you've entered contains a giant pit. Sticking up from the darkness of the pit's depths are dozens of pillars. Each looks to be a foot wide. From where you you stand the rows of pillars stretch back into the shadows beyond the illumination of your torches.

The Trap:It is now up to the PC reach the other side of the pit. Once a PC steps onto one of the pillars this trap activates. There are now five pillars to chose from. There is the one to the West of the PC's pillar. Another to the Northwest. A third one is directly North of the PC's pillar. Then there is a pillar to the North-East and a final one to the East.

Spoiler:

----X----
O O @ O O
O O O O O STEP 1

O O X @ O
O O O O O STEP 2

O O O X O
O O O O @ STEP 3

O O O O X
O O O O @ STEP 4

O O O O X
O O O @ O STEP 5

O O @ X O
O O O O O STEP 6

O = Pillar
X = Start
@ = Arrive

It is possible to walk across the pillars to the other side of the room. The first pillar sets a mechanism to WEST. Stepping onto another pillar sets the pillar to NORTHWEST. Then to NORTH, NORTHEAST, EAST, and back to WEST. Add in multiple PCs and reaching the other side becomes far more difficult. When a PC steps onto the wrong pillar watchout.

SLAM! A pillar slams down from the ceiling into the pillar that was just stepped on. After slamming down into it's counterpart the pillar in the ceiling returns to where it started from. The PC must manage to stay atop the pillar even after being smashed by pillar from the ceiling.

The Crunch:
CR -- TRAP (PILLAR SLAM PIT)
---------------------------------------
+0 -- Mechanical Trap
+0 -- Perception DC 15
+3 -- Disable Device DC 40
+0 -- REFLEX Save 17
+2 -- Attack Bonus +20 (Melee)
+1 -- Each Pillar deals 2d10+8 Damage (Bludgeon).
+1 -- Automatic Reset
+0 -- Bypass Mechanism

CR 7

Is this Challenge Rating correct? Should each pillar be considered a trap unto itself? Should this trap have a REFLEX Check?

Comments welcome. Advise sought.

[KissMeDarkly]

BUMP! BUMP! BUMP! BUMPER CARS!!

Still looking for some feedback on this. Preferably the kind that takes it apart bit by bit.