What is valley in plural form?

Valleys ...

because

if the noun ends in y + a,e,i,o,u ( a vowel letter) as in boy (y+o)

you do not cross out the y and add ies, you only add (s): boy+boys.... day =days,

BUT if the noun ends in y+ a consonant letter (b,c,d....), we cross the (y) and add "ies", as in baby=babies... lady=ladies