The Colorado National Monument Association writes that the two classes of units national parks and monuments differ primarily in the reasons for which they are established.
National parks are areas set apart by Congress for the use of the people of the United States generally, because of some outstanding scenic feature or natural phenomena.The principal qualities considered in studying areas for park purposes are their inspirational, educational, and recreational values.
National monuments, on the other hand, are areas preserved by the National Government because they contain objects of historic, prehistoric, or scientific interest. Generally established by presidential proclamation under authority of Congress, occasionally these areas also are established by direct action of Congress. (Source: NPS)
The recent change in designation from Pinnacles National Monument to Pinnacles National Park does not change the park’s management, or purpose. Congress specified in the 1970General Authorities Act and the 1978 Redwood Act that all units of the National Park System are to be treated on equal status, regardless of title. ( Source: Wikipedia)