Instead of PM, I'll just post it here since I don't need to do scaling or anything.

Okay, so a distance thrown of 30 Km, at a low-end angle of 45 degrees (Gets lowest results) gives us an initial velocity of 542.218 m/s. With this we can find an acceleration, but first we need the length of his arm.

An average man typically has a height of 1.80 m, and an arm length of .8 m.

1.80 / .8 = 2.25... if the cyclops is 91.44 m (300 feet) tall, then: 91.44 / 2.25 = 40.64 m, the length of his arm. If we assume he threw the rock in the way a baseball pitcher would (Makes it more low-end), he would have moved his arm a total of about 128 m

a = (v^2) / (2 * d)

542.218^2 / 2 * 128 = 1,148.439 m/s^2 the acceleration.

Next we need mass. 701.04 m circumference = 223.261 m, the diameter.

Height = 70.104 m.

Since it's dome shaped, I used this calculator and got a volume of 1,552,630.81 m^3

The density of rock is 2,700 Kg/m^3, so...

1,552,630.81 * 2,700 = 4,192,103,187 Kg, the mass of the rock.

F = ma

4,192,103,187 * 1,148.439 = 4,814,374,791,975.093 N, or 491,262,733.875 tons-force.

Quite impressive, though like I said, it's a bit rough due to the assumptions we had to make. Still gives you some idea of how strong he was.