Cinders were also a popular material to use for the track that surrounded HS football fields.
Of course, there were so many cinders around the 'Burgh, you also found em on all the ballfields too, football... baseball...
I still have cinders embedded in a scar on my right knee from a bad scrape I suffered 45 years ago when I was 13. I guess I didn't clean it up good enough before I painted it with
mercurochrome and slapped a bandaid on it.