150K Avios is enough for 2 returns in F with a 2-4-1. Last week I booked 2 x F to SFO in September next year. There was plenty availability to SFO, LAX, SAN, LAS & PHX provided you are flexible regarding a day or two either way and worth considering an open jaw ticket if dates are unsuitable. Will cost you circa. £591 each for taxes and charges.

West Coast USA is great at that time of year. Potential for some fog on the coast but 2 miles inland and the weather is great. Try SAN. a lovely city - motor up to Palm Springs where it will be really hot - but plenty to see and do! Spend some time in Los Angeles if you wish. All are within a 3 hour drive of each other.