If the era is January 1980 I'll take the cash. $100 worth of 1980 gold (bought with 1980 dollars) would be worth about $40 today.
$100 worth of gold bought at $850/ounce buys 0.117 ounces of gold. Today that gold (at $1181/ounce) is worth $138.90.
Your cash is worth $100.
The gold bull run of the 70s peaked at $850. So, even if you bought an ounce of gold at its peak, you'd be getting about $1300 for it today.
Cash, on the other hand, would have inflated away quite a lot, so your 100 bucks would buy you about 40 1980-dollars' worth of goods and services today.