Two things can cause squash (or melons or pumpkins) to have growth cracks.

The first is too much water as the fruit is ripening. As cooler temperatures signal the mature fruit to begin developing a hard skin, continuation of regular watering signals the fruit to keep growing. But since the skin is hardened, it can no longer get larger, so it will crack and the plant juices will ooze from these cracks. Cracks can be either horizontal or vertical, as seen in your photos, and the oozing juice can form some crystallization on the edges of the cracks. Watering should be reduced once squash skin begins to harden, however, note that even if watering is reduced but there is substantial rainfall during this time, you will still get growth cracks.

The other cause is applying nitrogen fertilizer at the incorrect stage of maturation. For the same reason as above, nitrogen signals the fruit to grow and expand, but the hard skin doesn't allow for expansion, thus cracking occurs. Vine crops such as these should be fertilized only as they begin to vine. If fertilization is necessary, apply only 2.5 ounces of nitrogen for each 250 feet of row. Fertilizing any later or with more than what is recommended will stimulate growth resulting in cracking.

More information on harvesting fall/winter squash:

http://planttalk.colostate.edu/topics/vegetables/1849-harvesting-fall-squash/