Big mammals include gemsbok, springbok, greater kudu, warthog, and giraffe. Hartmann's mountain zebra are the largest of Southern Africa's three races of zebra and occur only in western Namibia and southern Angola. The Naukluft massif was proclaimed as a park in 1968 specifically to protect them. On cold mornings they congregate on east-facing slopes to sun themselves. They are most active at dawn and dusk, spending the heat of the day in shade. They must drink daily and dig for water if necessary. Game viewing is at its best in the northern section of the park after summer rains result in lush grass. Large herds of animals congregate at this time. Game is less often encountered in the southern portion of the park and the mountains.