Removing red lava rock & amending soil

Hi, this is my first post to DG! I've enjoyed browsing threads the last month (actually year or two before I subscribed)... especially the pets thread - who wudda' thunk, I'd join a garden website & get waylaid by cute pets!

My question is: I have an area that currently has lava rock gravel. I planted some lantana on a slope next to the rock last year, and all of the plants inexplicably died! (I may not be the best gardener, but plants rarely die on me!). I assume the lava rock that had been kicked off the path into the dirt was the culprit - there was quite a bit of rock when I worked the soil, although I filled each hole with new soil. Now, I'm ready to landscape the whole area and am faced with the task of removing the rock and amending the soil.... and I'm gun shy after the lantana exprience.

Anyone have any experience/suggestions?

Thanks in advance!

Liz