Ik denk dat je de breedtegraad (37.780182) en lengtegraad (-122.517349) van je centrale punt hebt omgekeerd, probeer:
select
id,
hike_title,
lat,
lng,
( 3959 * acos( cos( radians(37) )
* cos( radians( lat ) )
* cos( radians( lng ) - radians(-122.517349) )
+ sin( radians(37.780182) ) * sin( radians( lat ) )
)
) AS distance
FROM
my_awesome_table
HAVING
distance < 10000
ORDER BY
distance
LIMIT
0 , 50