You can forage in the area around Moon Mountain everyday in Spring, Summer, and Fall. I suggest foraging when you first begin your game to boost your income early in the game. Items you find around Moon Mountain can be given to the Townspeople. It is a good way to increase your friendship with them without spending money. Just don't give Poisonous Mushrooms to anyone. Some recipes can only be acquired by giving people items you got from foraging.

Spring:
Edible Grass- 30 G
Flowers- Give it to the Girls
Medicinal Herbs- 70 G
Very-berry Berry- 40 G

Summer:
Edible Grass- 30 G
Flowers- Give it to the Girls
Medicinal Herbs- 70 G
Tropical Fruit- 40 G
Walnut- 70 G

Autumn:
Edible Grass- 30 G
Medicinal Herbs- 70 G
Mushroom (Brown)- 70 G
Poisonous Mushroom (Red and Yellow)- 30 G
Wild Grapes- 40 G

There aren't any items you can find around Moon Mountain in the Winter, so you have to go mining. The Mine is found near the Harvest Sprites' cave and is open from the 8th to the 30th. To start mining, just talk to the Carpenter outside the Mine. You have to have your Hoe with you to start digging, and you're stuck in the Mine until 5 P.M. or you run out of energy. If you encounter a hole while digging, go down it.

Winter:
Blue Stone- 700 G
Coin- 10 G (Deposited into your Gold Account immediately)
Iron Ore- 100 G
Moonlight Stone- 500 G
Pontana Root- 800 G
Rare Metal- 1000 G
Weathervane- Give it to Rick (Found on the Third Level)