Summary judgment was properly granted to defendant in this slip and fall case. Under Gov. Code 830 and 835, a governmental entity is liable for injuries caused by a dangerous condition of property only if the condition was caused by the entity’s negligence or the entity had actual or constructive knowledge of the condition. Here, plaintiff slipped on an ice patch in a parking lot. She could not prove that the city had actual knowledge of the ice patch. Nor could she show it had constructive knowledge of the ice patch since temperatures in the city varied from below to above freezing repeatedly over the days leading up to plaintiff’s fall. So there was no way to know when the ice patch formed. Constructive knowledge can be shown only when the condition has been present for a sufficient period to make it reasonable that the government entity should have discovered it.