Psalm 104:8 (ESV)

8 The mountains rose, the valleys sank down to the place that you appointed for them.

When the waters fled, the mountains appeared again, and the valleys became visible.

This is how God acted during creation (Genesis 1:9) and after the flood (Genesis 8:5).

Everything happened according to God’s plan, and so, the author of this psalm praises the Lord (see Psalm 104:1a and Psalm 104:35c!). The author encourages us to support him in his praise.