Rather near here was the Phoenix Research facility that quietly made arsine and phosphine gasses. There was quite an uproar when the general public realized that these extremely toxic gases were being manufactured right here in La Mesa! After much todo the plant shut down in 1989.
Googling the terms "poison gas" and "La Mesa" also led me to an autobiography of Frank Zappa, interestingly enough. Check it out!
Anyway, get yourself a berry sundae over at Costco, have a seat on the edge the sidewalk, watch the traffic go by, and feel around for the cache!
Please don't thrash the plants, they are starting to look pretty ragged!