What did The Bureau of the Census announce in 1890 had disappeared?

In 1890, The Bureau of the Census announced that the United States had officially reached a point where the frontier had disappeared. This declaration indicated that there was no longer a discernible line of settlement westward, marking a significant moment in American history as it reflected the country's westward expansion and settlement patterns. The announcement highlighted the end of an era characterized by the availability of unclaimed land for settlement.