Lichen present only at the base of a wall

Lichen present only at the base of a wall

Observation - Lichen present only at the base of a wall. Description: It seems a yellow crustose lichen species is present only at the bottom of the wall and next to it at the edge of the pavement. I'm not sure if the formation on the diamond pattern is lichen or algae. The pavement may also have a grey crustose species.

It seems a yellow crustose lichen species is present only at the bottom of the wall and next to it at the edge of the pavement. I'm not sure if the formation on the diamond pattern is lichen or algae.
The pavement may also have a grey crustose species.