Read the Ground
County records list expansive clay soils across the coastal plain. Clay shrinks and cracks open when dry, like the ground in the photo, and swells when wet. A slab on top rides that movement and cracks.
Fix the cause or the crack comes back.
Fix or Replace
A thin crack in a slab that has not moved can often be sealed. A lifted edge on a walk can sometimes be ground flat. A broken or sinking slab usually needs to come out. Ask for both prices when it is close.
Old Retaining Walls
A cracked or leaning retaining wall is a bigger job. National City lists retaining walls among the public improvements on its permit application. Ask the city before any wall work and ask if you need a soils report.
Questions
Why does concrete crack in National City?
Expansive clay soil is common in the coastal plain. It swells and shrinks with water and moves slabs.
Can a cracked walk be fixed instead of replaced?
Often, if the crack is thin and the slab is stable. A licensed contractor can tell you after a look.